Unit conversions you can actually trust
Type a number, get the exact answer. Every conversion on this site uses the official international factor, shows you the formula, and runs entirely in your browser.
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LiveThe values people look up most
Screen sizes, body height, gym weights and race distances — each with its own page, its own reference table and the arithmetic written out.
Screen sizes — inches to centimetres
Height — feet and inches to centimetres
Weight and distance
Guides that explain the number
A figure on its own is rarely enough. These guides cover why a 55-inch television is not 55 inches wide, why cups fail in baking, and where the 2.2 shortcut breaks.
TV & monitor screen sizes
What a screen size in inches actually measures, how wide each popular size really is, and how to check a TV fits before it arrives.
Height: feet, inches and cm
How to convert height between feet, inches and centimetres without the classic 5.10 mistake, plus a chart of common adult heights.
Weight: kg, pounds and stone
Convert body weight between kilograms, pounds and stone accurately — including why the 2.2 shortcut fails at higher weights.
Airline luggage limits
Cabin and checked baggage limits in both centimetres and inches, how airlines measure them, and where travellers get caught out.
Running distances
Every standard race distance in both miles and kilometres, with pace conversions and the splits runners actually use.
Baking measurements
Why cups fail in baking, how to convert American recipes to grams, and the tin sizes that change your bake most.
Built for accuracy, speed and privacy
Exact, not approximate
Every factor comes from the international definitions — 2.54 cm per inch, 0.45359237 kg per pound. Nothing is estimated.
Fast on any connection
No frameworks, no image carousels, no tracking pixels before consent. Pages are cached and typically weigh under 60 KB.
Private by design
Conversions happen in your browser. The values you type are never sent anywhere, stored or logged.
Measurement, explained properly
Practical articles about the numbers people get wrong most often.
Why your's new TV does not fit the space you measured
The number on the box is a diagonal, not a width — and the gap between the two is where returns come from. Two multiplications settle it before you order.
The 5.10 mistake: why decimal height conversions go wrong
Feet and inches look like a decimal number and behave nothing like one. Treating 5′10″ as 5.10 costs you nine centimetres.
The 2.2 shortcut is wrong, and sometimes it matters
Everyone multiplies by 2.2. The real factor is 2.2046226, and there are three situations where the shortcut costs you.
Common questions
Exactly 2.54. The inch was fixed at 2.54 centimetres by international agreement in 1959, so the conversion is exact rather than an approximation.
The maths runs at full precision and only the display is rounded, usually to two decimal places. Every page shows the formula so you can verify the number yourself.
No. Every converter and reference table is free, needs no sign-up, and runs entirely in your browser — the numbers you type never reach our servers.
The conversion factors are the official international ones, so they are correct. For anything safety-critical, always double-check against the specification you are working to.
Bookmark the converter you use most
Every value has its own page, so you can save it once and land straight on the answer next time.