About

The International Yard and Pound Agreement of 1959 defines 1 lb as exactly 0.45359237 kg. This makes the inverse factor 2.20462262185 lb/kg. Getting this wrong compounds across sets and reps in training logs, miscalculates shipping costs, and produces incorrect dosage-per-bodyweight figures in clinical contexts. A rough mental estimate of "multiply by 2.2" introduces up to 0.2% error, which across a 200 kg barbell load is nearly half a pound. This converter applies the exact NIST-traceable factor bidirectionally, with results to four decimal places by default.

The tool also provides a secondary readout in st lb (stones and pounds) for UK convention. Note: the avoirdupois pound is assumed throughout. Troy pounds (0.3732417216 kg) used for precious metals are a different unit entirely. All conversions here are for avoirdupois mass only.

Formulas

The conversion between kilograms and pounds is governed by the International Yard and Pound Agreement (1959), which defines the avoirdupois pound as an exact fraction of the kilogram.

m_lb = m_kg × 2.20462262185

The inverse conversion is:

m_kg = m_lb × 0.45359237

For the stones and pounds breakdown used in UK convention:

st = floor(m_lb ÷ 14)

remaining_lb = m_lb − (st × 14)

Where m_lb is mass in pounds, m_kg is mass in kilograms, st is whole stones, and 14 is the exact number of avoirdupois pounds per stone. The factor 2.20462262185 is derived from 10.45359237.

Reference Data

Kilograms kg	Pounds lb	Stones + Pounds st lb	Common Context
1	2.2046	0 st 2.2 lb	Standard bag of sugar (approx)
5	11.0231	0 st 11.0 lb	Dumbbell (light)
10	22.0462	1 st 8.0 lb	Bowling ball
20	44.0925	3 st 2.1 lb	Carry-on luggage limit
25	55.1156	3 st 13.1 lb	Olympic plate (standard)
45	99.2080	7 st 1.2 lb	Checked luggage limit
50	110.2311	7 st 12.2 lb	Cement bag
60	132.2774	9 st 6.3 lb	Light adult bodyweight
70	154.3236	11 st 0.3 lb	Average adult male (global)
80	176.3698	12 st 8.4 lb	Intermediate lifter bodyweight
90	198.4161	14 st 2.4 lb	Heavy adult bodyweight
100	220.4623	15 st 10.5 lb	Two-plate bench press
120	264.5547	18 st 12.6 lb	Super heavyweight class
140	308.6472	22 st 0.6 lb	Three-plate squat
180	396.8321	28 st 4.8 lb	Four-plate deadlift
200	440.9245	31 st 6.9 lb	Professional powerlifting range
500	1102.3113	78 st 10.3 lb	World record deadlift territory
1000	2204.6226	157 st 6.6 lb	One metric tonne

Frequently Asked Questions

The exact definition is 1 lb = 0.45359237 kg, making the inverse 2.20462262185... lb/kg. Using 2.2 introduces a 0.21% error. On a 100 kg load that is 0.46 lb off. Across a training cycle logging hundreds of sets, or in shipping where freight is billed per pound, these rounding errors accumulate into measurable cost or data inaccuracy.

Avoirdupois exclusively. Troy pounds (used for precious metals like gold and silver) equal 0.3732417216 kg - roughly 17.5% lighter than avoirdupois pounds. If you need troy conversions for bullion, this tool will give incorrect results. The avoirdupois system is the standard for bodyweight, food, shipping, and general commerce.

One stone equals exactly 14 avoirdupois pounds. The converter divides the total pounds by 14, takes the integer quotient as stones, and the remainder as residual pounds. This format is standard in UK medical records and everyday usage. For example, 80 kg = 176.37 lb = 12 st 8.4 lb.

No. Kilograms and pounds are both units of mass, not weight. The conversion factor is a fixed ratio defined by international agreement and is independent of gravitational field strength, temperature, or altitude. If you need to convert mass to weight-force (Newtons), you must multiply by local gravitational acceleration, which does vary with location.

Because 45 lb = 20.4117 kg and 20 kg = 44.0925 lb. Equipment manufacturers round to convenient numbers in each system independently. A bar loaded with 45 lb plates in a US gym is roughly 2% heavier than the same setup with 20 kg plates in a metric gym. Competitive powerlifting federations specify calibrated plates in kilograms (IPF standard) to eliminate this discrepancy.

For ingredient mass, yes. However, many recipes use volume measures (cups, tablespoons) which depend on ingredient density. Converting 500 g of flour to pounds (1.1023 lb) is exact, but converting cups to grams requires knowing the density of the specific ingredient. This tool handles mass-to-mass conversion only.