Preparing baby formula

Powdered infant formula is not sterile. This means you need to be careful when you're preparing a bottle for your baby. By following these steps you can reduce the risk of making your baby sick.


Breast milk is the best and most natural food for your baby. If you decide to formula feed, it is important that you always prepare your baby's bottle feeds safely.

What you need

To prepare formula milk correctly, you will need:

  • a clean work surface
  • at least 6 bottles, lids, discs and teats
  • formula milk
  • a safe water supply
  • a kettle
  • a bottle brush and a small teat brush
  • sterilising equipment like a chemical, steam or microwave kit
  • tongs to help you grip the equipment while sterilising

If you have a visual impairment, use wide-necked bottles. They are easier to fill.

You can use boiling water, a chemical steriliser or a steam kit to sterilise equipment.

A steam steriliser is the best. You can get plug-in or microwaveable sterilisers too.

How to make up a formula feed

  1. Empty your kettle and fill it with 1 litre of freshly-drawn cold tap water and boil. Alternatively, boil 1 litre of water in a clean pan.
  2. Leave the boiled water to cool in the kettle or pan. Cool it for 30 minutes, but no longer. This will make sure that the water is not too hot, but also that it is no less than 70°C.
  3. Clean the work surface well. Wash your hands with soap and warm water and dry them on a clean towel.
  4. Read the instructions on the formula’s label carefully to find out how much water and powder you need.
  5. Pour the correct amount of water into a sterilised bottle. Water that is 70°C is still hot enough to scald, so be careful.
  6. Add the exact amount of formula to the boiled water using the clean scoop provided. Reseal the packaging to protect it from germs and moisture. Adding too much or too little formula could make your baby sick.
  7. Screw the bottle lid tightly and shake well to mix the contents.
  8. To cool the feed quickly, hold the bottle under cold running water or place it in a large bowl of cold water. Make sure that the cold water does not reach above the neck of the bottle.
  9. To check the feed is not too hot, shake the bottle and place a drop of liquid on the inside of the wrist – it should feel lukewarm, not hot. Feed your baby.
  10. Throw away any feed that your baby has not taken within two hours. If your baby is a slow feeder use a fresh feed after two hours.
  11. After a feed, clean and rinse the bottle and teat.

Bottled water

You may need to use bottled water to make up feeds:

  • if you have a water softener system
  • have been told to boil all tap water before use
  • are on holiday abroad.

How to use bottled water:

  • use still water only, never fizzy or sparkling water
  • always boil the bottled water before using it to make up feeds
  • it is best not to use bottled water labelled as ‘natural mineral water’ as it can have higher levels of sodium and other minerals. It can be used if no other water is available, for as short a time as possible, as it is important to keep babies hydrated. 


Do not use tap water that has a water softener system. It may contain too much sodium.

The Food Safety Authority of Ireland (FSAI) does not recommend the use of formula preparation machines or automatic machines. There is not enough research to show these machines are safe and effective for preparing your baby's bottle.

How much formula your baby needs

This table is a guide only. Talk to your public health nurse (PHN) or GP if your baby is taking a lot less or a lot more formula than the amounts in this table.

Never re-use leftover milk once your baby finishes feeding. Throw the milk away after 2 hours.

At around 6 months you can start weaning your baby on to solid foods.

Your baby's age Number of feeds Amount of formula feed per baby weight
Birth to 3 months 6 to 8 (feeding every 3 to 4 hours) 150ml per kilogram (kg)2½ fluid oz (ounces) per lb (pound)
4 to 6 months 4 to 6 (feeding every 4 to 6 hours) 150ml per kilogram (kg)2.5 fluid oz (ounces) per lb (pound)

Vitamin D3 supplement for babies

You should give your baby 5 micrograms of vitamin D3 as a supplement every day from birth to 12 months if they are:

  • breastfed
  • taking less than 300mls or 10 fluid oz (ounces) of infant formula a day

All babies who are being breastfed should continue to get a vitamin D3 supplement after birth, even if you took vitamin D3 during pregnancy or while breastfeeding.

You do not need to give your baby a vitamin D3 supplement if they are fed more than 300mls or 10 fluid oz (ounces) of infant formula a day. This is because there has been an increase in the amount of vitamin D added to infant formula since 2020.

Read more about Vitamin D for babies 0 to 12 months

Measuring exact amounts of formula and water

It is important to measure the formula and water carefully. Too much or too little is not good for your baby.

For each 30mls (each ounce) of water, you need one level scoop of formula powder. Use the scoop in the formula box and run a clean knife across the top to level the scoop. For example, if you are making up a 90mls (3 ounces) feed, you will need to add 3 level scoops of formula to 90mls of cool boiled water.

Related content

Types of formula milk

Your breast milk is the best food for your baby, though you may decide to feed them formula milk. There are a few types of formula milk you can feed them.

Page last reviewed: 15 March 2018
Next review due: 15 March 2021