Weight Converter

Who it is for

This is for anyone reading a figure in one system and needing it in the other: a scale reading, a gym log, a parcel weight, a recipe quantity or a specification written for another market. It handles two units, not a general unit library.

The page opens with 1 in the kilograms field and 2.20 already in the pounds field, so the example is visible before you type. Nothing you enter leaves the page.

The factor and the rounding

Since 1959 the international avoirdupois pound has been defined as exactly 0.45359237 kilograms. That definition is exact by agreement, not measured, so the reverse factor is the recurring value 1 ÷ 0.45359237 = 2.2046226218… pounds per kilogram.

This page uses the shortened factor 2.20462. Kilograms are multiplied by it, pounds are divided by it, and the result is formatted to two decimal places:

Shortening the factor to six digits makes no visible difference at everyday scales: for every value up to about 1,000 kg the two-decimal display is identical to the one the exact definition gives. The gap only becomes visible on heavy loads. At 5,000 kg this page shows 11,023.10 lbs where the exact factor gives 11,023.11 lbs, and at 50,000 kg it shows 110,231.00 lbs against 110,231.13 lbs.

Accepted input is any finite number of zero or more. A negative number, or text the browser cannot read as a number, clears the other field and shows "Enter a valid non-negative weight." Emptying a field clears the other one rather than showing zero.

Mass or weight

Strictly, the kilogram and the pound used here are units of mass, while weight is the force gravity exerts on that mass and is measured in newtons. In everyday speech "weight" means the number a scale reports, which is a mass, and that is what this page converts.

Worked examples

1. 75 kg to pounds. 75 × 2.20462 = 165.3465, so the field shows 165.35 lbs.
2. 150 lbs to kilograms. 150 ÷ 2.20462 = 68.038936…, so the field shows 68.04 kg.
3. An edge case: 0.001 kg. 0.001 × 2.20462 = 0.0022, which rounds to 0.00 lbs. Any quantity under about 2.3 grams displays as 0.00, because the display is fixed at two decimal places rather than two significant figures.

Common conversions

The middle column is the unrounded product of the factor used on this page; the last column is what the field displays.

Starting from kilograms

Starting from pounds

Common mistakes

• Using 2.2 in your head. It is about 0.21 per cent low. At 70 kg that is 154.00 instead of 154.32 lbs — a third of a pound out, which matters for a luggage allowance or a shipping band.
• Expecting Switch to swap the numbers. It moves the cursor to the other field and selects what is there so you can type over it. The quantities stay where they are.
• Reading pounds as stones. British body weights are often quoted in stones and pounds. One stone is 14 pounds, so 11 st 4 lb is 158 lbs, not 11.4.
• Feeding the rounded answer into more arithmetic. Two decimals is enough to read, but if the figure goes into a further calculation, carry more digits from the unrounded product instead.
• Treating a conversion as added precision. If a scale reads to the nearest kilogram, converting to 165.35 lbs does not make the measurement finer than ±0.5 kg.

Limits

• Kilograms and pounds only. Grams, ounces, stones, tonnes, US tons and troy units are not offered.
• The output is always two decimal places, with no option for whole numbers or more digits.
• Negative quantities are rejected rather than converted.
• The recent list holds five entries, lives in the page's memory and is gone when you reload or close the tab.
• It is arithmetic, not metrology. For trade, customs, medical dosing or legal weighing, use the figure from a calibrated instrument and the rounding rule that applies to it.

Questions