About this tool
Why use this tool
Americans use pounds and ounces for body weight, food and shipping, while science, medicine (increasingly), international trade and fitness plans imported from Europe use kilograms and grams. Converting reliably matters for reading imported recipes (British bakes in grams), understanding international shipping rates, tracking medications dosed by weight, and following training plans by pro athletes who use metric.
How it works
1 pound (lb) = 0.45359237 kg exactly (1959 International Yard and Pound Agreement, codified by NIST). 1 kg = 2.20462 lb. 1 ounce (oz) = 28.3495 g. 16 oz = 1 lb. Troy ounce (used for precious metals: gold, silver) = 31.1035 g — different from the avoirdupois ounce used for everyday weight. Do not confuse them: a "gold ounce" is 10 % heavier than a food ounce.
Real example
A 150-pound person weighs 68 kg. A newborn at 7 lb 8 oz weighs 3.40 kg. A UK recipe calling for 500 g of flour needs 17.6 oz (about 1 lb 1.6 oz, or roughly 4 cups by volume). A 45 lb Olympic bumper plate weighs 20.4 kg — technically 0.4 kg more than a metric 20 kg plate.
Practical tips
For quick kitchen math: 1 lb ≈ 450 g; 1 oz ≈ 28 g; 1 stick of butter = 4 oz = 113 g. Use a digital kitchen scale with kg/lb toggle ($15 at Target). For infant weight, most US pediatricians (per AAP guidance) still report in pounds/ounces but chart in grams. For medication, always double-check with your pharmacist — pediatric dosing is per kg. Powerlifters: US Olympic bars are 45 lb (20.4 kg), IWF certified bars are 20 kg — check before matching PRs across gyms. USPS Priority Mail boxes are priced by lb; overseas via USPS International often uses kg.
Disclaimer
Conversions follow NIST exact ratios. For precious metals (gold, silver, platinum), always use troy ounces — the 10 % difference has cost buyers thousands. This tool is for general reference; commercial transactions require NIST Handbook 44 certified scales, and medical dosing requires clinical-grade equipment.