How to make up a formula bottle safely
Making up infant formula safely involves more than mixing powder and water. Powdered infant formula is not sterile, so the way it is prepared, cooled, stored and given can affect the risk of bacterial contamination (First Steps Nutrition Trust, 2026).
For standard powdered infant formula, NHS guidance recommends using freshly boiled water that has been allowed to cool for no more than 30 minutes, so that it remains at least 70°C when the powder is added (NHS, 2026a).
The 70°C temperature applies to preparation, not feeding. The hot water is used to reduce the risk from bacteria that may be present in powdered formula. The finished feed must then be cooled before it is offered to the baby because formula that is too hot can cause a burn (NHS, 2026a).
Why powdered formula should be made fresh
Powdered infant formula should be made up one feed at a time, as it is needed, rather than routinely preparing several bottles in advance and storing them in the fridge (NHS, 2026a; First Steps Nutrition Trust, 2026).
Powdered formula is not sterile and bacteria can be introduced through the powder, feeding equipment, hands or preparation surfaces. Once the powder has been mixed with water, bacteria can multiply if the feed is kept for a period of time (First Steps Nutrition Trust, 2026).
If feeding away from home, NHS guidance recommends taking the measured formula powder separately, together with an empty sterilised bottle and a full vacuum flask containing freshly boiled water. The feed can then be made up when it is needed (NHS, 2026b).
If this method cannot be followed, ready-to-feed liquid formula can be used instead (NHS, 2026b).
Powdered formula and ready-to-feed formula
Infant formula is available as powdered formula and as ready-to-feed liquid formula.
Powdered formula needs to be prepared carefully because it is not sterile. Ready-to-feed liquid formula is already prepared and does not need water or powder to be added (NHS, 2026c).
Ready-to-feed formula is sterile until opened. Once opened, it should be refrigerated and used according to the manufacturer's instructions. NHS guidance states that opened liquid formula should be used within 24 hours (NHS, 2026c).
This is different from formula left in a bottle after a baby has started drinking. Any formula remaining after a feed should be discarded rather than refrigerated for later use (NHS, 2026a).
Ready-to-feed formula does not need to be warmed if a baby is happy to drink it at room temperature. If it is warmed, it should be heated using warm water or a suitable bottle warmer and never in a microwave, which can create hot spots and cause burns (NHS, 2026c).
Before making up a powdered formula feed
Bottles, teats, caps and other feeding equipment need to be thoroughly cleaned and sterilised before use. Hands and the preparation surface should also be clean (NHS, 2026a; UNICEF UK Baby Friendly Initiative, 2022).
For information about cleaning and sterilising feeding equipment, see:
If a cold-water sterilising solution has been used, follow the steriliser manufacturer's instructions. NHS guidance advises shaking off excess solution and, where rinsing is required, using cooled boiled water rather than tap water (NHS, 2026a).
Why does the water go into the bottle first?
The correct amount of water should be measured into the sterilised bottle before the formula powder is added.
This is important because adding formula powder changes the final volume of the feed. The powder occupies space within the water and, once dissolved, increases the volume of the prepared feed. Measuring the water first therefore provides the correct starting volume for the manufacturer's formula-to-water ratio.
The amount of water and powder varies between products, so always follow the instructions for the particular formula (NHS, 2026a).
Many standard powdered formulas use approximately one level scoop for every 30 ml of water, but this is not universal. The manufacturer's instructions take precedence.
How to make up a powdered formula feed
The following reflects NHS guidance for standard powdered infant formula. Specialist formulas may have different preparation instructions.
1. Use fresh cold tap water. Fill the kettle with at least 1 litre of fresh water from the cold tap. Do not use previously boiled water or artificially softened water (NHS, 2026a; First Steps Nutrition Trust, 2024).
2. Boil the water. Allow the boiled water to cool in the kettle for no more than 30 minutes so that it remains at least 70°C when the powder is added (NHS, 2026a).
3. Clean the preparation area and wash your hands. Clean and disinfect the surface being used before preparing the feed (NHS, 2026a; UNICEF UK Baby Friendly Initiative, 2022).
4. Prepare the sterilised bottle. Keep the teat, cap and other components in a clean place rather than directly on the work surface.
5. Measure the water first. Pour the correct amount of hot water into the bottle and check the level carefully before adding any powder (NHS, 2026a; First Steps Nutrition Trust, 2024).
6. Add the formula powder. Use the scoop supplied with the formula and follow the manufacturer's instructions exactly. Scoops should be level rather than heaped (NHS, 2026a).
7. Mix the feed. Assemble the bottle and shake or mix according to the manufacturer's instructions until the powder has dissolved.
8. Cool the feed. Hold the bottle, with the lid securely in place, under cold running water. A sealed bottle can also be stood in a container of cold water to help it cool (NHS, 2026a).
9. Check the temperature. Place a few drops on the inside of the wrist. The feed should feel warm or cool rather than hot (NHS, 2026a).
10. Give the feed when it is ready. Powdered formula should be prepared fresh rather than routinely prepared in advance (NHS, 2026a).
11. Discard leftovers. Any formula remaining after the baby has started drinking should be thrown away (NHS, 2026a).
The UNICEF UK Baby Friendly Initiative Guide to Bottle Feeding also provides guidance on preparing formula and sterilising feeding equipment (UNICEF UK Baby Friendly Initiative, 2022).
Why should powdered formula be prepared with water of at least 70°C?
Powdered infant formula cannot be assumed to be sterile. Using water at a temperature of at least 70°C when reconstituting powdered formula is intended to reduce the risk from bacteria that may be present in the powder (First Steps Nutrition Trust, 2026).
The temperature needs to be considered at the point when the water and powder are combined. Research examining formula preparation in UK homes found that water dispensed by formula preparation machines was frequently below 70°C, potentially allowing bacteria in powdered formula to survive (Grant et al., 2024).
The finished feed should then be cooled before feeding. The 70°C preparation temperature and the cooler drinking temperature serve different purposes.
Formula preparation machines
Formula preparation machines use a different process from the NHS method of preparing powdered formula with freshly boiled water that remains at least 70°C when the powder is added (NHS, 2026a).
Some use a fixed-volume "hot shot" before cooler water is added. The amount of hot water therefore represents a different proportion of the feed depending on its size, while the final drinking temperature is not the same as the preparation temperature needed to reduce bacterial risk.
The original Perfect Prep was investigated by BBC Watchdog in 2016 after concerns about bacterial contamination, with bacteria found in water from some machines tested. Research published subsequently has also found that formula preparation machines do not consistently deliver water at or above 70°C (Grant et al., 2024).
Filters, cleaning and descaling also need consideration. Filter use varies considerably according to how frequently a machine is used and the size of the bottles being prepared. A machine used for around eight feeds a day for a newborn will process considerably more water than one used once a day for a toddler, even though a calendar-based filter replacement period may be similar. Hard-water areas can also result in greater mineral build-up and a greater need for descaling.
There have also been reports of black or mould-like material inside some machines. These reports were investigated separately, with the manufacturer stating that the material was carbon residue associated with filtration rather than mould (Sky News, 2017).
A preparation machine should therefore not automatically be considered equivalent to the NHS kettle method simply because it produces a bottle quickly at a suitable drinking temperature.
Rapid-cooling devices
Rapid-cooling devices are designed to cool freshly prepared powdered formula quickly.
Current First Steps Nutrition Trust guidance advises against relying on these devices until they have been independently tested and shown to be safe. Its concern is that rapid cooling reduces the time the powdered formula is exposed to heat, potentially allowing bacteria to survive. Additional containers and handling steps can also introduce further opportunities for contamination (First Steps Nutrition Trust, 2026).
The current recommendation remains to prepare powdered formula using freshly boiled water that has cooled to no less than 70°C, then cool the prepared bottle under cold running water before feeding (First Steps Nutrition Trust, 2026; NHS, 2026a).
A rapid-cooling device should not therefore be treated as a replacement for the hot-water preparation step.
What about hot-water or boiling-water taps?
Hot-water and boiling-water taps should not automatically be assumed to be equivalent to the NHS kettle method.
The important consideration is the temperature of the water when it is combined with the powdered formula. First Steps Nutrition Trust has shown that the temperature of water from a hot tap can fall relatively quickly once it has been transferred into a bottle, particularly with smaller volumes (First Steps Nutrition Trust, 2019).
Different taps will also produce different temperatures, so a hot tap cannot simply be assumed to provide water at the temperature required for preparing powdered formula.
First Steps Nutrition Trust also advises caution with baby kettles that repeatedly reboil water to maintain temperature, as repeated boiling may concentrate some elements in the water (First Steps Nutrition Trust, 2019).
Fresh water and the manufacturer's preparation instructions should always be used.
Cooling and checking the finished feed
Once the powdered formula has been mixed with the hot water, it needs to be cooled before feeding.
The bottle can be held, with the lid securely in place, under cold running water. It can also be stood in a container of cold water to help it cool (NHS, 2026a).
Some bottle systems have vents or other openings, so care is needed to ensure that water cannot enter the bottle during cooling. Follow the manufacturer's instructions for the particular feeding equipment.
Check the finished feed by placing a few drops on the inside of the wrist. It should feel warm or cool rather than hot (NHS, 2026a).
There is no requirement for every baby to drink formula at exactly the same temperature. The important consideration is that the feed is not hot enough to cause a burn.
Never microwave infant formula because it can heat unevenly and create hot spots (NHS, 2026a).
Making formula away from home
Powdered formula should still be prepared fresh when it is needed when feeding away from home.
NHS guidance recommends taking a measured amount of formula powder in a clean, dry container, an empty sterilised bottle and a clean vacuum flask containing freshly boiled water. If the flask is full and sealed, the water should remain above 70°C for several hours (NHS, 2026b).
The feed can then be prepared when it is needed rather than preparing bottles in advance.
If the recommended method cannot be followed, NHS guidance advises using ready-to-feed liquid formula instead (NHS, 2026b).
How much formula does a baby need?
The amount of formula a baby takes can vary considerably. Babies may want different amounts at different feeds and may feed little and often. Responsive feeding means responding to the baby's feeding cues rather than expecting every feed to be the same size or requiring a bottle to be finished (NHS, 2026d; UNICEF UK Baby Friendly Initiative, 2022).
First Steps Nutrition Trust provides approximate guidance on the amounts of infant formula that may be offered at different stages. These figures are based on average energy requirements and average infant weights and are not targets for individual babies (First Steps Nutrition Trust, 2020).
| Age | Approximate feeds | Approximate amount per feed | Approximate total per day | |---|---:|---:|---:| | Up to 2 weeks | 7–8 feeds | 60–70 ml | 420–560 ml | | 2–8 weeks | 6–7 feeds | 75–105 ml | 450–735 ml | | 2–3 months (9–14 weeks) | 5–6 feeds | 105–180 ml | 525–1,080 ml | | 3–5 months (15–25 weeks) | 5 feeds | 180–210 ml | 900–1,050 ml | | About 6 months (26 weeks) | 4 feeds | 210–240 ml | 840–960 ml | | 7–9 months | Breakfast, lunch, tea and before bed | About 150 ml | About 600 ml | | 10–12 months | Breakfast, tea and before bed | About 100 ml, 100 ml and 200 ml | About 400 ml |
These are approximate figures rather than required volumes. Babies vary in appetite and feeding patterns, particularly during the early weeks, and some may need smaller feeds more frequently (First Steps Nutrition Trust, 2020).
For information about responding to a baby's cues during bottle feeding, see Responsive Bottle Feeding.
Bottle position and support can also affect how comfortably a baby feeds. See Bottle Feeding Positions.
Different types of formula may have different preparation instructions
There are several types of infant formula, and the preparation instructions are not necessarily identical.
First infant formula is suitable from birth and can remain the main formula throughout the first year. Follow-on formula is not required at six months (NHS, 2026c).
Specialist formulas can have different preparation instructions. Anti-reflux formulas, for example, contain thickening ingredients and some products require a period of standing after preparation because the feed thickens. Some manufacturers also give different instructions about the temperature of the water used to prepare these products (NHS, 2026c).
This means that the instructions for the particular formula being used should always be followed rather than assuming that the standard preparation method applies to every product.
Specialist formulas used under medical supervision should be prepared according to the instructions supplied with the product or by the relevant healthcare professional.
The key distinction: preparation temperature and feeding temperature
The temperature of formula matters at two different points for different reasons.
During preparation, water at or above 70°C is used with powdered formula to reduce the risk from bacteria that may be present in the powder.
Before feeding, the prepared formula must be cooled so that it is not hot enough to burn the baby's mouth.
A feed therefore needs to be hot enough during preparation for the safety process to be effective, but cool enough afterwards for safe feeding.
Further information
The UNICEF UK Baby Friendly Initiative Guide to Bottle Feeding provides guidance on preparing infant formula and sterilising feeding equipment (UNICEF UK Baby Friendly Initiative, 2022).
First Steps Nutrition Trust: Making infant milk safely provides further information about powdered infant formula, preparation machines and alternative preparation methods (First Steps Nutrition Trust, 2026).
References
First Steps Nutrition Trust (2019) Making up bottles of infant formula from hot taps and baby kettles. London: First Steps Nutrition Trust.
First Steps Nutrition Trust (2020) Infant milks: A simple guide to infant formula, follow-on formula and other infant milks. London: First Steps Nutrition Trust.
First Steps Nutrition Trust (2024) Infant milks: A simple guide to infant formula, follow-on formula and other infant milks. London: First Steps Nutrition Trust.
First Steps Nutrition Trust (2026) Making infant milk safely. London: First Steps Nutrition Trust. Available at: https://www.firststepsnutrition.org/making-infant-milk-safely
Grant, A., Jones, S., Sibson, V., Ellis, R., Dolling, A., McNamara, T., Cooper, J., Dvorak, S., Breward, S., Buchanan, P., Yhnell, E. and Brown, A. (2024) ‘The safety of at home powdered infant formula preparation: A community science project’, Maternal & Child Nutrition, 20(1), e13567. doi:10.1111/mcn.13567.
NHS (2026a) How to make up a bottle feed. NHS Best Start in Life. Available at: https://www.nhs.uk/best-start-in-life/baby/feeding-your-baby/bottle-feeding/how-to-make-up-a-feed/
NHS (2026b) Formula milk: common questions. NHS. Available at: https://www.nhs.uk/baby/breastfeeding-and-bottle-feeding/bottle-feeding/formula-milk-questions/
NHS (2026c) Types of formula milk. NHS. Available at: https://www.nhs.uk/baby/breastfeeding-and-bottle-feeding/bottle-feeding/types-of-formula/
NHS (2026d) How to bottle feed. NHS. Available at: https://www.nhs.uk/baby/breastfeeding-and-bottle-feeding/bottle-feeding/
Sky News (2017) ‘Tommee Tippee investigates reports of “mould” in formula machines’, 15 March. Available at: https://news.sky.com/story/tommee-tippee-investigates-reports-of-mould-in-formula-machines-10802939
UNICEF UK Baby Friendly Initiative (2022) Guide to bottle feeding: How to prepare infant formula and sterilise bottles. UNICEF UK Baby Friendly Initiative. Available at: https://www.unicef.org.uk/babyfriendly/baby-friendly-resources/bottle-feeding-resources/guide-to-bottle-feeding/ ```
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