Kitchen Scale Accuracy, Resolution and Calibration

Kitchen scales are sold on two numbers, the capacity and the smallest step the display shows, and a third idea, accuracy, is easy to confuse with them. This guide explains what the terms mean, when a 1 g step is enough and when you want 0.1 g, how to check a scale at home with UK coins, and why a kitchen scale is the wrong tool for medicines. It is general information for adults. For the full buying checks, see our buying guide.

What the words on the specification mean

Adam Equipment, a scale manufacturer, publishes a glossary of these terms. We have put them in our own words:

• Capacity: the most the scale can carry. The bowl counts towards it.
• Readability (the smallest step): the size of the finest division the display shows. This is what a listing means by "1 g increments" or "0.1 g".
• Accuracy: how closely the displayed value matches the true value of a known weight.
• Repeatability: whether the scale gives the same reading each time you put the same weight on it.
• Linearity: whether readings stay correct from light loads up to the maximum.

The glossary notes that these terms are often used interchangeably, yet it defines them separately: readability is about the display's division, and accuracy is about matching a known weight. A display that shows 0.1 g has a finer division, which does not by itself show that the last digit is right. The Tanita KD-400 and KD-320 pages give a single figure labelled "accuracy" (1 g and 0.1 g), and the Salter Toronto page says "1g increments", so those figures read as the size of the step. We did not find a statement on any of the three pages of how readings were checked against a known mass.

What the law checks

GOV.UK's guidance on the Non-Automatic Weighing Instruments Regulations 2016 says regulated instruments, including those used to sell by weight or to dispense prescription medicines, must meet essential requirements and carry UKCA or CE and M marks. Domestic kitchen and bathroom scales are non-regulated, so under these Regulations they are not conformity assessed and do not need the weighing-instrument marks. They must show the manufacturer's name and address and the maximum capacity. For a kitchen scale, then, the accuracy claim is the maker's own, and checking it is up to you.

When 1 g is enough, and when it is not

If a display rounds to the nearest gram, a reading of 5 g could stand for anything from 4.5 g to 5.5 g. For energy, the size of that error depends on the food. Using McCance and Widdowson's Composition of Foods (CoFID), a half-gram error is about 4.5 kcal for olive oil (899 kcal per 100 g), about 3 kcal for smooth peanut butter (607 kcal per 100 g) and about 2 kcal for white sugar (394 kcal per 100 g). Over a day's cooking that is small next to the other uncertainties, and the labels themselves give average values. For most food tracking, 1 g steps are enough.

A 0.1 g step earns its place for small amounts of strong ingredients:

• Salt and spices. The NHS says adults should have no more than 6 g of salt a day, around one level teaspoon, so a 1 g step is a large share of a day's limit.
• Supplement scoops. A 3 g serving on a scale that rounds to the nearest gram could be anywhere from 2.5 g to 3.5 g, a swing of about 17% either way, while a 0.1 g scale narrows it to 2.95 g to 3.05 g.

Check the capacity too. Tanita lists its 0.1 g KD-320 at 3 kg and its 1 g KD-400 at 5 kg. Here are searches for kitchen scales that read to 0.1 g on Amazon (opens in a new tab) and digital pocket scales on Amazon (opens in a new tab); pocket scales are a separate category, so read the capacity on the listing.

A home accuracy check with coins

The Royal Mint publishes the weights of new coins in its coin-set listings: 20p 5.00 g, 50p 8.00 g, £1 8.75 g and £2 12.00 g. Coins that have been in circulation may weigh slightly less than the new-coin figures (our caution, not a Royal Mint statement), so treat this as a rough check, and use several coins.

1. Zero. Put the scale on a firm, level surface and switch it on. It should read zero with nothing on it.
2. Known masses. Weigh one 50p, then a 20p, then both. Expect 8, 5 and 13 g on a 1 g scale, and values close to 8.0, 5.0 and 13.0 g on a 0.1 g scale.
3. Range. Add coins in steps. Ten £1 coins come to 87.5 g, so expect 87 or 88 g on a 1 g scale and about 87.5 g on a 0.1 g scale, with the readings rising in step with the coins you add.
4. Repeatability. Weigh the same coin three times, then again near each edge of the platform. The readings should agree.
5. Tare. Put a bowl on, press tare and add a coin. You should see the coin's weight alone.

If your scale has a calibration mode, the manual says what mass to use. Sets of calibration weights are sold for this, and the class and tolerance stated on the listing matter more than the headline mass: calibration weights on Amazon (opens in a new tab) is a search for them. If a new scale fails these checks after you have fitted a fresh battery, GOV.UK says sellers must offer a full refund for an item that is faulty or not as described.

Supplement powders and dosing

The FSA advises you to always read the label and follow the warnings and instructions, not to take more than the recommended dose, and not to take high-dose supplements unless a GP or healthcare specialist advises it. Use the scoop or measure supplied. If you want to check how much a level scoop holds, weigh it on a 0.1 g scale several times and compare with the weight on the label, as our guide to how to take creatine suggests. Doses measured in micrograms are far below what a 0.1 g display can show, so a scale cannot help with those.

A kitchen scale is also not a pharmacy instrument. GOV.UK lists weighing to dispense prescription medicines among the regulated uses, so do not use a kitchen scale to measure medicines. Follow your pharmacist's directions.

Cautions

Accurate numbers do not make weighing food right for everyone. The NHS advises talking to a GP or healthcare professional before you make changes to your lifestyle to lose weight if you have a medical condition, a special diet or an eating disorder or have had one, and says weighing portions is not something you have to do for ever. If measuring food starts to feel stressful, stop and speak to a GP.

The instructions that come with your scale are the authority on its capacity and care, and the label on a supplement is the authority on its dose. Ask a GP or pharmacist if you take medicines or have a health condition.