KKoumen Tools PRO

Every unit, one screen.

Metric and US side by side. Type once, read every conversion at the same time.

Converting units without a lookup table

Unit conversion is simple arithmetic with two traps: temperature is not a multiplication, and precision beyond the input is meaningless. Both are handled here.

  1. Pick a category. Length, weight, temperature, area, volume and speed each have their own set. Mixing categories is the most common conversion error, so they are kept apart deliberately.
  2. Enter a value and the unit you have. Type the number as you have it. The conversion happens as you type, with no button to press.
  3. Read the result in the unit you want. The other units in the same category update too, so you can see that 12 inches is both 1 foot and 30.48 cm without doing three conversions.
  4. Round sensibly. The result keeps enough precision to be useful and no more. Converting 5 miles gives 8.04672 km, which is exact, but converting a rough measurement does not become exact by being displayed to five decimals.

When this comes up

Questions

Why is temperature conversion different from the others?

Because Celsius and Fahrenheit have different zero points, not just different-sized degrees. The formula is (F − 32) × 5/9, which is a shift and a scale. Doing a simple multiplication gives an answer that is wrong by a fixed 32 degrees, which is exactly the kind of error that looks plausible.

Is a US fluid ounce the same as an imperial one?

No, and the difference is about 4%. A US fluid ounce is 29.57 ml; an imperial (UK) fluid ounce is 28.41 ml. A US pint is 473 ml, a UK pint is 568 ml. The same word means different amounts, which is why a British beer order and an American one are not the same volume.

How precise should a converted value be?

Never more precise than the original. If you measured something to the nearest inch, the metric equivalent is accurate to about 2.5 cm, regardless of how many decimals are displayed. Extra digits imply a precision the measurement does not have.

What is the difference between mass and weight?

Strictly, mass is the amount of matter (kilograms) and weight is the force gravity exerts on it (newtons). In everyday use, and on Earth, they are treated as the same thing, which is why scales are marked in kilograms. On the Moon your mass would be unchanged and your weight would be a sixth of it.

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