100 pound to kilogram
Full conversion table below. Use the calculator to convert any other value or unit pair.
Pound to Kilogram
45.359237
Result
100 pounds equals 45.359237 kilograms.
Common unit comparison (log scale)
A Brief History of Weight Measurement
Weight measurement traces back to ancient Babylonian and Egyptian records, which show weight originally measured by the capacity of containers like gourds or clay and metal vessels. Seeds became early standardized reference weights — the carat, still used for gemstones today, takes its name and original definition from the remarkably consistent weight of carob seeds.
The British Imperial system — pounds, ounces, stone — descended from Roman and Arab measurement traditions (the word "ounce" comes from the Latin uncia) and was formally standardized in the 1824 Weights and Measures Act. The metric system, developed by French scientists in the late 18th century, instead uses clean base-10 relationships — one kilogram was originally defined as the mass of one liter of water.
Full Conversion Table
| Unit | Value |
|---|---|
| Kilogram (kg) | 45.359237 |
| Gram (g) | 45359.237 |
| Milligram (mg) | 45359237 |
| Metric Ton (t) | 0.04535924 |
| Pound (lb) | 100 |
| Ounce (oz) | 1600 |
| Carat (ct) | 226796.185 |
| Atomic Mass Unit (u) | 27316613670581150255947003914 |
| Grain (gr) | 700000 |
| Stone (st) | 7.142857 |
| Quarter (UK) (qr) | 3.571429 |
| Hundredweight (US) (cwt) | 1 |
| Hundredweight (UK) (cwt) | 0.8928571 |
Metric vs. Imperial Weight
The metric system's mass units (milligram, gram, kilogram, metric ton) scale cleanly by powers of 1,000, making unit conversion within the system a matter of moving a decimal point. Imperial and US customary units (grain, ounce, pound, stone, hundredweight) instead use historical ratios — 16 ounces to a pound, 14 pounds to a stone — that require explicit conversion factors like the ones this calculator applies.
Why US and UK Hundredweight Differ
A US ("short") hundredweight equals 100 pounds, while a UK ("long") hundredweight equals 112 pounds — a holdover from the historical British avoirdupois system that the US customary system simplified when it diverged from imperial units.
Specialized Units
The carat (used for gemstones) and the atomic mass unit (used in chemistry and physics for atomic and molecular masses) exist because everyday units like the gram are far too large for convenient use at those scales — a single atom's mass in grams would require dozens of leading zeros.
Weight vs. Mass
Strictly speaking, these units measure mass — the amount of matter in an object — not weight, which is the force gravity exerts on that mass. On Earth's surface, the distinction rarely matters day-to-day, but it explains why an object's mass in kilograms stays constant even though its weight would differ on the Moon.
Example — Your Current Inputs
100 pounds equals 45.359237 kilograms.
Additional Example — Recipe Conversion
A recipe calling for 250 grams of flour needs about 8.82 ounces, or just over half a pound — a common conversion for anyone following a metric recipe with an imperial kitchen scale.
About These Parameters
- Value
- The quantity you want to convert, in the "From" unit selected below it.
- From & To Units
- Any of the 13 supported mass units, spanning everyday units (kilogram, pound) to specialized ones (carat, atomic mass unit). The full conversion table above shows your value in every unit at once.
Frequently Asked Questions
How many pounds are in a stone?
One stone equals exactly 14 pounds — a unit still commonly used for body weight in the UK and Ireland.
Is a US ton the same as a metric ton?
No — a US short ton (2,000 lb ≈ 907.18 kg) is lighter than a metric ton (1,000 kg ≈ 2,204.62 lb), which in turn is lighter than a UK long ton (2,240 lb ≈ 1,016.05 kg). This calculator uses the metric ton.
Why is a carat exactly 0.2 grams?
The carat was standardized to exactly 200 milligrams (0.2 grams) internationally in 1907, replacing slightly varying regional definitions that had been based on the average weight of a carob seed.