Heating Baby Bottles

Maths: To heat a baby milk bottle safely using the perfect combo of hot and cold water

The following method for warming a baby bottle, is a milk heating method using hot and cold water.  Its based on 37 Degrees Celsius temperature (blood temperature) which is the same temperature as breast milk. If you follow this method precisely (based on mathematics) then its easy to prepare the perfect temp for baby.  I’m doing this example for a 200mL bottle serving -but do check your formula tin for serving size for your baby’s age and then how much powder to add at the end.

This is based on 6th form maths!!

Franny x

1. Keep a large jug of previously boiled-then-cooled water in the fridge at 4 Degrees Celsius.  Ensure that you tip un-used water out of the jug after 12 hours and that you thoroughly wash the jug before adding more water.

2. Make some boiling hot water, at 100 degrees Celsius with your kettle or pot.

3. Have all your bottle equipment already cleaned and sterilised.

The following simultaneous equation tells you how much volume of boiling water (at 100 degrees) to add with how much volume of cold water (at 4 degrees) to get a warm safe mixture of water at 37 degrees, for a 200mL baby bottle.  You can then add your formula powder to the bottle, shake up, and give to baby to drink.

Make x = mLs of 100 degree water

and y = mLs of cold water and z = final mixture then:

x + y = z

100x + 4y = 37z

we know z = 200mL for baby to drink

so x + y = 200

y = 200 – x


100x + 4y = 7400

100x + 4(200-x) = 7400

100x + 800 – 4x = 7400

96x = 6600

x = 68.7 mLs of 100 degrees boiling water water

y = 131.3mLs of 4 degrees cold water

4. Add the boiling hot water 68.7 mls. Then add 131.3 mLs of cold water. Add the required formula dose. Shake well.

5. Always refer to the formula tin for the dose to feed baby.

6. Always check temperature before feeding to baby. It should feel the same temperature as your skin.

7. Remember never to re-heat baby’s milk (i.e don’t reheat leftovers next time).   And don’t heat milk in a microwave.