How to use
Choose a unit type such as Length or Area. The common units are listed first, and a link from search opens its type directly.
Type a number in any unit. Every unit of the same type is converted at the same time, and you can type into any row.
Pick 4, 6 or 10 significant digits. The default is 10, and trailing zeros are removed.
Open “Definition and source” under a unit to read its formula. Where a unit is based on a law or a published standard, its source is given too.
Use the quick table for typical values, and the copy button on a row to copy one value.
What it does
Every unit of a type at once
Type a number in one row and every unit of that type updates: metres, feet, inches, shaku, ken and ri for length, or tsubo, m², tatami by standard, tan and chō for area. You can type into any row.
Exact fractions, rounded only for display
Each unit is held as an exact ratio to its base unit (for example 1 inch = 0.0254 m and 1 tsubo = 400/121 m²). No floating-point error is used; results are rounded to the chosen significant digits.
Tatami shown by standard
A tatami varies by region and standard, so the real-estate advertising basis (1 tatami = 1.62 m² or more) and the typical Kyoma, Chukyo, Edoma and Danchi sizes each have their own row.
Temperature and fuel follow their formulas
°C, °F and K use the offset formulas (affine), and L/100 km is the reciprocal of km/L. A temperature below absolute zero and a fuel economy of 0 are reported as errors.
A definition and source for each unit
Open “Definition and source” under any unit to read its formula. Units based on a law or a published standard give the source, and units that need care in trade have a note.
Use cases
- Convert a flat size from tsubo to m² to compare with a floor plan
- Estimate the area of a room from its number of tatami mats
- Convert US or UK sizes (inches, pounds, °F) to metric
- Measure a recipe’s go or tablespoon amounts in millilitres
- Compare fuel economy figures written as km/L, L/100 km or mpg
Capability matrix
| Feature | Support | Notes |
|---|---|---|
| Length, area, weight, volume (cooking), temperature, speed, fuel economy and energy | Supported | — |
| Tatami (each standard gives a different value; the size varies by region and building) | Partial | Typical sizes, not a legal definition |
| Traditional Japanese units (shaku, tsubo, kan, go and others) | Partial | Whether they may be used in trade or certificates depends on the Measurement Act. Reference only |
| Currency conversion (exchange rates) | Not supported | Exchange rates need a network connection, so they are not handled here |
| Data size conversion (MB, GB and so on) | Not supported | See the related IT Calculator below |
| Date and time conversion | Not supported | See the related Date & Time Studio below |
| Input in exponent form, such as 1e3 | Not supported | Type digits, a decimal point and a sign |
Limits & notes
- Input is limited to 40 characters. Results can show 4, 6 or 10 significant digits (default 10).
- Negative values are accepted for temperature (°C and °F) only. A temperature below absolute zero (0 K) is an error.
- A fuel economy of 0 (L/100 km or km/L) cannot be converted.
- Very large or very small results (below 1e-9 or 1e18 and above) are written in exponent form, such as 1.5e+18.
- Units not listed here, and national or local units that are not on the list, are not included.
Privacy & safety
Numbers you type are calculated only in your browser. Nothing is sent to or stored on a server, and the numbers are not put in the URL (only the unit type is).
FAQ
How do I convert tsubo to square metres?
How many square metres is a tatami mat?
How many millilitres is one go?
How do I convert inches to centimetres?
What is the formula for Fahrenheit to Celsius?
How accurate are the results?
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