Formula Tin Calculator: How Long Does a Tin of Formula Last?

Parents often ask how many days one tin of formula will last, or how many tins to buy. The answer is not the same for every baby or every brand, so this calculator uses your own numbers: the weight of the tin, the amount of powder your tin says makes 100 ml, and how much milk your baby drinks in a day.

It is a planning tool for shopping, not feeding advice. How much milk your baby needs, and how to make a feed up safely, come from your tin's instructions, your health visitor and the NHS (see below).

How the calculator works out the days

1. Powder used in a day (g) = milk your baby drinks in a day (ml) ÷ 100 × grams of powder per 100 ml.
2. Days a tin lasts = tin net weight (g) ÷ powder used in a day (g).
3. Made-up milk per tin (ml) = tin net weight (g) ÷ grams of powder per 100 ml × 100.
4. Tins per 30 days = 30 ÷ days a tin lasts.

The sums use net weight, which is the weight of the powder alone and is printed on the tin as, for example, 800 g. Your baby's milk will usually go up as they grow, so run the sums again every few weeks. To see what a typical daily amount looks like for your baby's weight, use the formula amount calculator.

Why tins say different amounts of powder

Different formulas come with different scoops and different mixing tables. The NHS says to follow the manufacturer's instructions very carefully, because they vary as to how much water and powder to use, and to use only the scoop that comes with the formula, levelled off with a clean, dry knife or the leveller provided.

The NHS also says not to add extra formula powder when making up a feed, because this can make your baby constipated or dehydrated, and not to add extra water, because too little powder may not give your baby enough nourishment. So the calculator never changes the amount of powder per feed. It only counts how long the powder you use will last.

To reduce the risk of infection, the NHS says it is best to make up feeds one at a time, as your baby needs them, and to throw away any made-up formula left in the bottle after a feed. Planning how many bottles a tin makes is fine, but do not mix several feeds ahead because of it.

What if my tin lists scoops?

If your tin's preparation table is written in level scoops rather than grams, the calculator still needs grams, so you have two options:

• Ask the brand how many grams one level scoop of your formula holds, then multiply it by the number of scoops that go into 100 ml.
• As a rough shortcut for planning only, look at the nutrition table on the tin. It often has a column per 100 g of powder and a column per 100 ml made up. Divide the energy per 100 ml by the energy per 100 g and multiply by 100 to estimate the grams of powder in 100 ml.

Treat the shortcut as an estimate. Always make up feeds exactly as the preparation table on your tin says.

How long can an opened tin be kept?

Use the rule printed on your own tin. The UK pages for Aptamil First Infant Milk (800 g and 1.2 kg) say to use the powder within 4 weeks of opening, and to store it in a cool, dry place and not in the fridge. The SMA First Infant Milk page gives the same 4 weeks for its 400 g, 800 g and 1.2 kg sizes. If the calculator shows that a tin lasts longer than your tin's label allows once opened, a smaller tin may fit your baby better.

The NHS adds that even sealed tins and packets of powdered infant formula can sometimes contain bacteria, which is why it recommends making up each feed fresh, with water that has been boiled and left to cool for no more than 30 minutes so it is still at least 70C.

Tin sizes sold in the UK

The size buttons above come from the brands' own UK product pages for first infant milk powder: Aptamil First Infant Milk in 700 g, 800 g and 1.2 kg; SMA First Infant Milk in 400 g, 800 g and 1.2 kg; and Kendamil Classic First Infant Milk in 800 g. They are product facts, not a recommendation of any brand. If your tin shows a different net weight, type it in.

Frequently asked questions