Unit Converter
Convert between the most common length, weight, temperature, area, and volume units in seconds. Just type a number and all results update instantly.
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How to Use
① Select a category — Length, Weight, Temperature, Area, or Volume. ② Enter a number in the input field and pick the source unit from the dropdown. ③ All conversions update instantly as you type — no submit button needed. ④ Use the Copy button to copy all results to your clipboard at once.
The row matching your source unit is highlighted so you can confirm what you entered at a glance. Clearing the input resets all results to '—'.
How the Conversion Works
Length, weight, area, and volume all use a base-unit factor table and simple multiplication. For length the base is the meter (m): 1 mm = 0.001 m, 1 km = 1000 m, 1 inch = 0.0254 m (exact), 1 mile = 1609.344 m (exact). The formula is: result = input × (from_factor / to_factor). Because the yard–pound definitions were fixed against the metric system in the 1959 International Yard and Pound Agreement, the conversion factors are exact, not approximations.
The 1959 International Yard and Pound Agreement also fixed the pound: 1 lb = 453.59237 g exactly. The common approximation '1 pound ≈ 450 g' understates the true value by about 0.9% — closer to 453.6 g. For cooking or shopping where produce is sold by the pound, that ~3.6 g difference per pound can add up noticeably over larger quantities.
Temperature is different because each scale has a different zero point. Celsius (°C) sets 0 at the freezing point of water and 100 at boiling. Fahrenheit (°F) was originally based on a salt-ice mixture (0 °F) and human body temperature (roughly 100 °F), later standardized so that water freezes at 32 °F and boils at 212 °F. Kelvin (K) starts at absolute zero (the coldest theoretically possible temperature, −273.15 °C), making it the natural scale for thermodynamics. Converting between them requires both multiplication and addition: °F = °C × 9/5 + 32, K = °C + 273.15.
Volume units use the US liquid system (1 cup = 236.588 mL, 1 gal = 3785.41 mL). These differ from the metric cup (250 mL) used in Australia and Canada, and from the Japanese cooking cup (200 mL). If a recipe specifies 'cup' without noting the region, check which system it uses.
Frequently Asked Questions
- How many square meters is one tsubo (坪)?
- One tsubo equals exactly 400/121 m² ≈ 3.30579 m². The tsubo is a traditional Japanese area unit equal to the area of a square with sides of one ken (間), which is 6 shaku. Because one shaku is defined as 10/33 of a meter, the conversion produces the repeating fraction 400/121. Japanese real estate listings that use tsubo are required by law to also state the area in m².
- How many mL is 1 US cup?
- Exactly 236.5882365 mL. This is around 18% more than the 200 mL Japanese cooking cup and about 5% less than the 250 mL metric cup used in Australia and Canada. When following an American recipe, use this tool to convert cups to mL if you are measuring with a metric cup.
- How accurate is the approximation '1 mile ≈ 1.6 km'?
- One mile is exactly 1609.344 m. Using 1.6 km gives an error of 0.344 m (0.021%), and using 1.61 km gives an error of 0.656 m (0.041%). For casual distance estimation the 1.6 km approximation is perfectly fine, but for sports timing, surveying, or aviation you need the exact value. A handy curiosity: 5 miles is almost exactly 8 km (5 × 1609.344 = 8046.72 m), which explains why 5 km races and 5-mile races feel similar.
- Why does 1 inch equal the awkward number 0.0254 m?
- Before 1959, the inch was defined slightly differently in the US and the UK. The 1959 International Yard and Pound Agreement set 1 yard = 0.9144 m exactly, which means 1 foot = 0.3048 m and 1 inch = 0.0254 m. The number looks 'awkward' in meters only because it was derived from the yard, not the other way around. In the yard–pound system, 12 inches per foot and 3 feet per yard are the clean numbers; the metric equivalent is the derived value.