Precision Weight & Mass Converter | Fast & Accurate

Why weight conversion trips everyone up

Weight is the most common unit conversion people search for — kilograms to pounds, grams to ounces, stones to kilograms. The catch is that the world uses three overlapping systems: metric (kg, g, mg), imperial / US customary (lb, oz, st, tons), and specialty units (carats for gems, grains for ammunition and medicine). Each has its own definitions, and mixing them up is how cooking recipes fail and luggage gets flagged at the airport.

This converter uses NIST-defined conversion factors based on the international avoirdupois pound (1 lb = 0.45359237 kg), so every result lines up with what shipping labels, customs forms, and food packaging actually use.

Common weight conversions

The two conversions people actually need every day are kilograms ↔ pounds and grams ↔ ounces. Memorise the row that matches your usual range — everything else is just multiplication.

How to convert weight manually

• The 2.2 rule (kg to lb). Multiply kilograms by 2.2 for a quick estimate, or by 2.20462 for shipping-grade precision. Going the other way, divide pounds by 2.20462.
• Metric powers of ten. Every metric step is ×1000. There are 1,000 grams in a kilogram, 1,000 milligrams in a gram, and 1,000 kilograms in a metric tonne. Move the decimal — no calculator needed.
• Stone (UK body weight). 1 stone is exactly 14 pounds, or about 6.35 kilograms. To go from stone to kg, multiply by 6.35029. To go from kg to stone, divide by 6.35029.
• Tons differ. A metric tonne is 1,000 kg (~2,204.62 lb). A US short ton is 2,000 lb (~907.18 kg). A UK long ton is 2,240 lb (~1,016.05 kg). They are not interchangeable — always check which "ton" a document means.

Specialty units worth knowing

• Carats (ct). Used only for gemstones and pearls. 1 ct = 0.2 g. A one-carat diamond weighs 200 milligrams. Not to be confused with karat (gold purity), which is unitless.
• Grains (gr). The oldest unit in the imperial system. 1 gr ≈ 64.8 mg. Still used for bullet weights, arrow weights, and pharmaceutical dosing (aspirin tablets are historically 5 grains ≈ 324 mg).
• Troy weight. A separate system used for precious metals (1 troy ounce ≈ 31.1035 g, heavier than an avoirdupois ounce of 28.3495 g). This converter uses avoirdupois — do not use it to weigh gold bullion.

Five mistakes everyone makes

• Confusing weight and mass. On Earth they're interchangeable in daily life. On the moon, 1 kg of flour still has 1 kg of mass — but weighs about a sixth as much.
• Mixing US and UK tons. A "ton" in a British text usually means a long ton (2,240 lb). In a US text it means a short ton (2,000 lb). The 240 lb gap matters for freight.
• Using 1 kg = 2.2 lb for customs. Close enough for the gym, but 2.20462 is what shipping carriers and customs forms expect. A 50 kg shipment is 110.23 lb, not 110.
• Mixing avoirdupois and troy ounces. A jeweler's ounce (troy) is ~10% heavier than a kitchen ounce (avoirdupois). For gold pricing, always specify.
• Forgetting the carat decimal. Carat values are usually written with two decimals (1.25 ct, not 1¼). Rounding to 1 ct loses 20% of the weight.

Unit reference table

Frequently asked questions