Writer Jessica Bernhard researched 25 bottle warmers and spent more than 10 hours testing nine of them in early 2024. She also spoke with doctors and lactation consultants about how to safely prepare breast milk and formula. Jessica has a decade of editorial experience and formerly served as an editor for REI Expert Advice, where she reviewed hundreds of outdoor products. She is the mom to two young children, including a 12-month-old who consumes multiple bottles daily.

This guide builds on the work of Wirecutter senior editor Courtney Schley, a mom of four, who first reviewed bottle warmers for Wirecutter in 2017. She warmed more than 50 bottles of formula and breast milk in six models to determine the best one. Courtney also interviewed leading experts, including a physician from the American Academy of Pediatrics and a representative with the Infant Nutrition Council of America.

Some babies are happy drinking cold breast milk or formula, and there isn’t good evidence to suggest that they benefit more from breast milk or formula that’s been heated. “It’s really okay to feed your baby cold milk,” said Amelia Henning, certified nurse midwife and director of the Mass General Lactation Program. “For many parents, not having to warm up a bottle in the middle of the night can make a big difference.” (Neonatologists are interested in understanding whether warm milk or formula may benefit preterm infants or babies who are sick, but more research is needed in this area.)

But a bottle warmer can be a helpful tool for caregivers of bottle-fed babies who prefer their milk or formula heated up, and may be particularly convenient for families of multiples and day care center workers who need to heat more than one bottle in a row.

Most warmers feature a heating element and timer that warms bottles to around 98 °F (about body temperature). Milk or formula that’s heated to higher than body temperature may burn the baby’s mouth or body, and heating breast milk above 104 °F can alter its bioactive properties, explains Ashley E. Wofford Leong, a family practice physician who specializes in infant feeding. In many cases, it can be just as efficient to heat milk or formula in a water bath filled with hot water (150 °F) from a kettle, or by holding the bottle under warm, running water.

Some warmers, including our top pick, the Kiinde Kozii, can also heat frozen pouches of breast milk (though we don’t suggest it) and containers of baby food. Others, like our budget pick, The First Years Simple Serve, double as sterilizers for pump and bottle parts. This can help you stay on top of all the work of keeping bottles and accessories clean for each feeding. If you’re looking for recommendations for bottles, see our guide to the best baby bottles and bottle brush.

Based on our research, we determined a good bottle warmer should:

Heat milk efficiently, without overheating: A good bottle warmer reliably heats milk or formula without overheating or developing hot spots. It’s possible to overheat a bottle in any warmer by choosing too lengthy of a cycle, or by leaving the bottle in the warmer for an extra minute or two. This is because even warmers with an auto-shutoff remain warm, though not hot. To avoid burns and altering the bioactive properties of breast milk, the best bottle warmers do not allow milk or formula to exceed 104 °F. It takes approximately 7 minutes 30 seconds to heat an 8-ounce bottle of refrigerated formula using a bowl of hot water (about 150 °F); we looked for warmers that came close to that time.

Fit a range of bottle types: Babies can be fickle, and some go through a period of preferring one bottle shape or size over another. The best bottle warmers accommodate a range of bottle types, models, shapes, sizes, and materials, including short, squat bottles; narrow-neck bottles; and those made from plastic, silicone, or even glass.

Be intuitive to use: Simple-to-set timers and controls, and a clear signal to let you know when the heating cycle is complete, make bottle warmers easier to use. The best ones have an automatic shutoff and/or internal thermostat that prevents bottles from becoming too hot.

Allow back-to-back cycles: A bottle warmer that accurately and efficiently heats more than one bottle in quick succession without having to unplug, add cold water, or wait to let the heating element cool is helpful for busy, tired parents of multiples or two kids under 2 years old.

Be relatively easy to clean: All bottle warmers require some care in order to avoid mineral buildup from tap water. The process varies; most require that you clean the interior with warm, soapy water every two to three days and descale the unit by filling it with a mixture of water and distilled white vinegar every two to four months.

Provide a good value: Baby gear can be pricey and may only come in handy for one to two years. We looked for ones that are durable enough to be resold or saved for use with a future baby.

In early 2024, we tested nine bottle warmers using four of the leading bottle brands and models. We first evaluated the bottle warmers to see how easy each was to assemble and use. We then noted whether they accommodate a range of bottle types, and whether they could also heat frozen breast milk pouches and baby food.

We next put the bottle warmers through a test using a probe thermometer. We prepared and refrigerated the formula until it reached between 40 °F and 50 °F. We filled small bottles with 4 ounces of formula and large bottles with 8 ounces of formula. At the beginning of each heating cycle, we placed the probe near the center of each bottle, halfway deep into the liquid. We then tracked the temperature of the formula as it heated, recording the temperature every 30 seconds. At the end of each cycle, we recorded the temperature at the surface of the milk (the surface temperature tended to be several degrees warmer than the center, as warmer liquid rises above cooler liquid) and the time it took to heat the bottle. In researching safe use, we learned that bottle warming should never take more than 15 minutes to guard against possible bacteria growth, according to the experts we interviewed.

We next swirled the bottle gently five times and took the temperature at the center of the milk. We finally gently shook the bottle for about 30 seconds more and noted the final temperature. (Most warmers instruct you to swirl the bottle for 30 seconds after the machine’s cycle ends.)

Once we narrowed the field to two top warmers, we used them to heat bottles of breast milk. We found that breast milk bottles heated at similar speeds to formula bottles.

Of all the bottle warmers we tested, the Kiinde Koziii did the best job of warming baby formula to around 98 °F (our expert-recommended temperature) without overheating. The device turns on with the twist of a dial that works (and ticks) like a kitchen timer, which means you ultimately control how long you expose your baby’s milk or formula to heat. It’s not inexpensive, and the cleaning process is involved. Still, the Kozii’s reliable heating and simple interface set it apart from every other bottle warmer we’ve tested over the years.

It’s more efficient and reliable than other warmers. The Kozii does a better job of quickly warming bottles to the ideal, 98-degree temperature than any other model we’ve tested. It heated a plastic 4-ounce Philips Avent bottle to 98 °F in just 6 minutes, and a plastic 8-ounce Lansinoh bottle in 8 minutes 30 seconds. We consider this to be successful, given that you can heat breast milk or formula to a similar temperature in 7 minutes 30 seconds in a bowl of hot water from a kettle—and preparing water in a kettle takes additional time.

When we originally tested the Kozii in 2017, we found it was faster than competitor models, except for steam warmers like an earlier version of The First Years Simple Serve. There are now some models (like the Philips Avent Premium Fast Baby Bottle Warmer) that use a water bath to heat formula more rapidly than the Kozii, but they aren’t as accurate or consistent.

A water reservoir reduces the chance of overheating. The Kozii is the only model we tested that uses a circulating water bath, as opposed to the still water bath seen in other water-bath warmers. The water recedes into a reservoir at the base of the device as soon as the heating cycle is complete and then the device turns off, which means you’re less likely to overheat bottles using the Kozii than with other models. In only one instance during our 2024 testing, the Kozii came close to overheating a glass, 4-ounce Evenflo bottle with a final temperature of 101 °F.

It has the most effective auto-shutoff of any model we tested. Part of the appeal of a bottle warmer is that you can tend to another task—like changing a diaper or making coffee—while the device does its work. But warmers without an auto-shutoff require constant supervision, since leaving the bottle on the warmer for even one additional minute can cause the contents to become dangerously hot. The Kozii's auto-shutoff is unlike any other on the market. The entire machine shuts off after the heating cycle and, unlike with other water-bath warmers, the water recedes, so the heat source is removed. (Though you can still overheat bottles if you miscalculate the heating time or leave the bottle in the device for a long time even after it’s turned off.)

Competitor models with a more traditional auto-shutoff, like The First Years Simple Serve (our budget pick) and Kiinde Kozii SafeHeat Pro, expose bottles to residual heat even once they’ve turned off. Several other models we tested only shut off after 45 minutes or one hour, which is too long to expose milk or formula to heat because bacteria can develop.

You don’t have to fill the Kozii with water every time. This is one of the easiest warmers to use because it doesn’t require measuring a precise amount of water. You add water to the basin so it rises above the pump valve and turn the dial to the appropriate setting for the bottle you want to warm—this is a more simple process than setting a digital timer on competing models. Another perk: You don’t need to empty the device of water after each use.

You can fine-tune the heating cycle. The manual includes a reference chart of approximate warming times when setting the dial. Once you get a feel for how long it takes to heat your baby’s bottles, the user-interface is easy to program. You can set the dial to the anticipated warming time and make minor adjustments in 30-second increments.

It’s also easy to add another minute or two after the cycle is complete if, after sampling the temperature of the milk or formula on your skin, you find the need to heat the bottle a little longer. And the fact that the dial counts down like a kitchen timer means you always know how long you have to wait before your baby’s bottle is ready.

It’s compatible with most bottle types. You can use the Kozii with narrow-neck, wide-neck, silicone, plastic, and glass bottles from many leading brands.

It can heat bottles back-to-back. Many bottle warmers require you to add cool water and/or wait up to 10 minutes between heating cycles. With the Kozii, caregivers can prepare one bottle after another; per the instructions, you simply reduce subsequent heating cycles by 30 seconds.

Flaws but not dealbreakers

The signals could be more clear. Some warmers have blinking lights and beeps to indicate the heating cycle is complete. The Kozii makes a subtle ticking sound throughout the heating cycle; the end of the ticking means your bottle is ready. We would prefer a more obvious indicator.

We don’t recommend using the Kozii to heat frozen breast milk. The Kozii easily accommodates frozen breast milk pouches, but we found it heats them unevenly. During testing, some portions of our milk reached more than 120° F, whereas other areas remained frozen.

The cleaning process is involved. The instruction manual says to clean the Kozii every two to three days by emptying the water chamber and refilling it with a cup of fresh water mixed with mild soap. Every two months, it calls for descaling the Kozii by mixing a half cup of white vinegar with 1 cup of water and pouring the mixture into the machine. You let it sit for 10 to 20 minutes, empty it, and rinse it. And one Wirecutter staffer who has owned the Kozii for two years noted that there isn’t a way to dissemble the machine to really scrub or wash it.

The First Years Simple Serve Baby Bottle Warmer and Sanitizer heats formula rapidly without overheating, but it lacks many of the conveniences of our main pick. Its steam-heating method means that sometimes bottles come out feeling hot to the touch, and steam can build up in the nipple. Still, we think it’s a solid choice for caregivers who don’t mind some effort to find the right heating time.

It’s efficient. This was the fastest and most accurate of the steam warmers we tested. (Our top pick, the Kiinde Kozii, heats bottles via a circulating water bath, not steam). We love that the Simple Serve gets the job done quickly, heating 4-ounce plastic bottles in a little over 3 minutes (the Kiinde Kozii took 6 minutes).

But it doesn’t work with glass bottles. Like our top pick, this warmer fits many types of bottles, and it comes with a thin, plastic adapter to help hold narrow bottles in place. However, a warning in the manual says because the Simple Serve heats bottles rapidly, it cannot be used with glass bottles, as a sudden temperature change could cause the glass to break. (We found this a bit odd since the warmer can also be used to heat jars of baby food.)

An auto-shutoff helps avoid overheating bottles. Pressing an “on” button starts the heating plate, causing the water to boil and release steam to heat the bottle. A green light on the Simple Serve switches off to let you know that the cycle is complete. As with our top pick, the auto-shutoff helps you avoid overheating bottles, but it’s still relatively easy to do, especially if you miscalculate heating times or leave a bottle unattended.

Maintaining the Simple Serve is easier than with the Kiinde Kozii. To clean the warmer, you wipe the surface of the unit and the inside of the warming chamber with a mild, soapy water, then air-dry. Every two to four months, you descale the unit to prevent mineral buildup by filling the warming chamber with a small amount of distilled vinegar followed by a clean-water rinse.

Flaws but not dealbreakers

It takes some trial and error. As with our top pick, to get started, you consult a chart with heating times based on bottle size, shape, and milk or formula temperature. You then add a small amount of water to a small plastic vial (the amount dictates the length of the heating cycle) and then pour that water into the warming chamber. We were initially confused by the chart, which denotes heating times for narrow-neck versus wide-neck bottles. We weren’t sure if a 4-ounce Philips Avent bottle, for instance, would be considered narrow or wide. We ultimately found that adding about a half-unit less water than recommended worked best for the bottles in our test, though we would have had trouble gauging this without a digital thermometer. It took us two to three tries to get the correct amount of water and thus the proper heating time.

The plastic vial is difficult to fill. This is the biggest drawback of the Simple Serve: The measurement lines on the tiny plastic vial you must fill with a precise amount of water are difficult to read, especially in the middle of the night.

It can’t heat bottles in quick succession. You cannot use the Simple Serve to heat multiple bottles in a row, instead you have to wait 10 minutes in between cycles.

It can’t heat frozen breast milk. Its steam mechanism means you cannot use it to heat frozen breast milk pouches. You can use the Simple Serve to heat baby food and to sterilize pacifiers and bottle parts, but it only fits one or two parts at a time. Some pump parts may not fit at all.

If you want a warmer that calculates the length of the heating cycle for you: The Tommee Tippee Multiwarm Intuitive Bottle Warmer has a simple user interface and an internal thermostat that controls how long bottles are exposed to heat. You select the heating cycle based on the bottle material, size, and milk or formula temperature using buttons on the machine rather than by cross-referencing a chart. During testing, heating cycles ranged from 5 minutes 30 seconds for a 4-ounce glass bottle to 9 minutes for an 8-ounce plastic one. The Tommee Tippee lacks a countdown clock or timer, so you’re often left wondering when your bottle will be ready. Three loud beeps let you know once the heating cycle is complete. Heating times can be difficult to predict, too. In one instance the Tommee Tippee heated a 4-ounce plastic bottle in 9 minutes and an 8-ounce plastic bottle from the same brand in 8 minutes. Its wide design means it fits a variety of bottle brands, models, shapes, and sizes.

If you want a portable bottle warmer for airplane or car travel: The USB-powered Baby’s Brew 3.0 Portable Bottle Warmer Pro does a good job of heating milk and formula on the go, and it’s compact enough to stash in a diaper bag or carry-on. Several leading bottle brands, including Philips Avent, screw onto the top of the Baby’s Brew, and many other brands work with adapters that are available for an additional cost. If you don’t have the correct adapter, the warmer may leak. A digital interface on the front of the warmer lets you select from a range of target temperatures. Once the heating cycle begins, you swirl the bottle every so often. This is more work, but it allows for consistent warming. Warming times varied. And the Baby’s Brew wasn’t as consistent as our picks in its warming abilities—some bottles only reached room temperature, whereas others reached 98 °F.

You can easily heat bottles of formula and breast milk without a bottle warmer in roughly the same amount of time it takes our pick, the Kiinde Kozii, to do the job.

The first thing we’d suggest to anyone new to warming bottles is to first try placing the bottle with the desired amount of breast milk or formula in a bowl of hot water that’s been heated in a kettle, submerging as much of the bottle as possible. We filled a bowl with 3 cups of water that was around 150 °F. Once immersed, it took 6 minutes 30 seconds for a 4-ounce refrigerated bottle of formula to warm to about 98 °F, and 7 minutes 30 seconds for an 8-ounce bottle to heat to that temperature. If you use this option, check to make sure the water is the correct temperature before submerging (some kettles indicate temperature as they heat, but an instant-read thermometer also works well); placing a bottle of milk or formula in boiling water can cause the bottle to quickly overheat.

The other option is to hold the bottle under warm, running water for a few minutes, gently swirling the bottle to heat it evenly. Tap water in homes in the US typically tops out around a recommended 120 °F. We found it took about 5 minutes to heat a refrigerated 4-ounce bottle of formula to around 98 °F, and about 8 minutes 30 seconds to heat an 8-ounce bottle. A downside is that this method wastes a lot of water—two gallons or more, in our tests—and requires you to stand at the sink for 5 or more minutes (you could also just place the bottle under a stream of hot water, though it will take more time to heat if you’re not also swirling the liquid).

No matter how you warm the bottle, gently swirl it after warming and test the temperature of the liquid by placing a few drops on the inside of your wrist before feeding it to a baby. The milk or formula should be no warmer than body temperature (it should feel tepid rather than warm on your skin). Check that no part of the bottle or nipple is too warm for the baby to touch, and that no steam has built up in the nipple reservoir.

The Centers for Disease Control and Prevention (CDC) and the experts we consulted say you should never heat bottles in the microwave, as it can lead to hot spots in the milk, allow steam to build up in the nipple, or make the bottle explode. You should also not warm bottles in boiling water, or directly on the stove, which can cause bottles to overheat.

Regardless of how you heat formula or breast milk for a baby, the final serving temperature should be around 98 °F, or cooler. This is ideal because it’s around body temperature and is also cool enough to be free from any risk of burning a baby’s mouth or body.

When heating breast milk, remember that it’s a living substance, said Mass General’s Henning. “You really don’t want to get up over about 100 degrees because you begin to see significant decline in the anti-infective properties of the milk.”

Always follow manufacturer instructions when preparing baby formula, which typically doesn’t have the same heat sensitivities as breast milk (though formula enhanced with probiotics, for example, can be compromised when exposed to high heat). To protect against cronobacter, the CDC advises that you mix powdered formula with water that has been heated to at least 158 °F to kill bacteria that could be present in the powder. You must then wait for the formula to cool before serving it. Liquid-concentrate formula and ready-to-feed formula do not need to be prepared with hot water.

The experts we spoke with told us that warming all types of breast milk and formula should take less than 15 minutes to reduce the opportunity for possible bacteria to grow.

We were excited by the streamlined interface of the Philips Avent Premium Fast Bottle Warmer, but it had a tendency to overheat glass bottles. The Avent’s auto-shutoff activates after one hour, which our experts say is too long since bacteria can develop in heated breast milk or formula after 15 minutes.

The First Years Digital Baby Bottle Warmer has an accessible price (about $35), but it took too long to heat large bottles, with some taking up to 14 minutes. This is too long given concerns about bacteria.

The Kiinde Kozii SafeHeat Pro features the same intuitive interface as our top pick, with a stainless steel warming chamber that uses a traditional warm-water bath. Unfortunately, the device overheated all of the bottles in our test to higher than body temperature.

The Babymoov Duo Smart Bottle Warmer seemed like a smart pick for caregivers who might use a warmer at home and on the go, given its portable nature. But we decided not to test it after we learned it didn’t fit leading bottle brands, including those from Philips Avent and Comotomo.

Many caregivers swear by the Baby Brezza formula dispensers for preparing bottles of formula. We tested the Baby Brezza Safe & Smart bottle warmer, which offers both a quick (steam) and steady (water bath) warming mode. Unfortunately, it consistently overheated bottles to concerning temperatures.

We also eliminated the Grownsy 8-in-1 Fast Milk Warmer early in our testing as it began malfunctioning in the middle of a heating cycle.

In 2017, we elected not to test the Philips Avent Fast Bottle Warmer because BabyGearLab found it quickly overheated bottles.

We also didn’t test the Boon Orb bottle warmer in 2017, because BabyGearLab found it quickly overheated bottles, and you also can’t use it with glass bottles.

This article was edited by Amy Miller Kravetz and Kalee Thompson. Courtney Schley wrote an earlier version of this guide, first published in 2017.