Unit Converter

Type one number and the whole family appears at once. No more converting inches to centimetres, then centimetres to feet, one step at a time.

Length

Tap any row to copy it. Figures are rounded for reading, but the value copied is the full precision one.

The ones a table can't do

Three conversions people actually get stuck on.

Height — cm ↔ feet and inches

Heights come as 5'9", not as a decimal. Converting the inches on their own gives the wrong answer.

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Body weight — kg ↔ pounds and stone

In the UK and Ireland body weight is given in stone and pounds together.

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TV and monitor inches → real width

Screen sizes are the diagonal. What you need for a shelf or a mount is the width.

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Why inches and centimetres line up exactly

One inch is exactly 2.54 cm. It is not a convenient rounding — the 1959 international yard and pound agreement, signed by the US, UK, Canada, Australia, New Zealand and South Africa, defined the inch as 25.4 mm. The same agreement fixed the pound at 0.45359237 kg. That is why inches, feet, yards, miles, pounds and ounces mean the same thing wherever you are.

Worth memorising: 1 foot = 30.48 cm, 1 yard = 91.44 cm, 1 mile = 1.609 km, 1 pound = 453.6 g, 1 ounce = 28.35 g. And back the other way: 1 cm ≈ 0.394 in, 1 m ≈ 3.28 ft, 1 km ≈ 0.621 mi, 1 kg ≈ 2.205 lb.

The gallon is not one thing

Length and weight are settled. Volume is not. A US gallon is 3.785 L, an imperial gallon is 4.546 L — more than 20% apart. The US gallon comes from the old English wine gallon, while the imperial gallon was redefined in 1824 as the volume of ten pounds of water. Two different ancestors, two different sizes.

This bites hardest on fuel economy. A car rated at 30 mpg does about 12.75 km/L on the US gallon but only 10.6 km/L on the imperial one. Fluid ounces differ too: 29.57 mL in the US, 28.41 mL in the UK.

Getting a feel for °C and °F

The exact formula is °F = °C × 9/5 + 32, but for a rough read, double it and add 30. At 20 °C that gives 70 °F against an actual 68 °F — close enough to know how to dress.

A few anchors help more than the formula. Freezing is 0 °C / 32 °F. Room temperature 20 °C / 68 °F. Body heat 37 °C / 98.6 °F. Boiling 100 °C / 212 °F. A hot summer day at 90 °F is 32 °C, and 100 °F is 38 °C. One quirk worth knowing: −40 °C and −40 °F are the same temperature.

Stone, and why UK weights read oddly

A stone is 14 pounds, about 6.35 kg. In Britain and Ireland body weight is normally spoken as stone plus pounds — "twelve stone four" rather than 172 pounds or 78 kg. Converting to a single decimal loses the form people actually use, so this page gives you both.

The unit survives in everyday speech even though official contexts went metric decades ago, which is why a British scale often shows all three at once.

TV inches are the diagonal

Screen sizes measure corner to corner. A 55 inch set has a 139.7 cm diagonal, and on a 16:9 panel that comes out around 121.8 cm wide by 68.5 cm tall. Estimating the width from the diagonal leaves you roughly 20 cm short.

Bezels and the stand foot add further width, so before buying a wall mount or a media unit check the outer dimensions the manufacturer publishes. Ultrawide monitors stretch this gap further — same diagonal, far more width.

The figures behind this page

Working with precious metals instead? Troy ounces are a different unit again — see the gold price calculator.