Methodology & Sources

One rule above all: a weight is only published when we have opened a public, authoritative source and copied its figure verbatim. If no qualifying source exists, the object is not published — it goes on our data-gaps list instead. We never fill gaps from memory or estimation.

Source hierarchy, best first: (1) standards and rules bodies — NIST, ISO, IWF, World Athletics, US Mint, LBMA; (2) government and research institutions — USGS, NOAA, NASA, USDA, CDC, WHO, EPA, national park services; (3) museums, zoos and universities; (4) manufacturer specification pages; (5) peer-reviewed papers; (6) established encyclopedias such as Britannica. Wikipedia is never the only source — it can help us find the primary one. Competitor sites, content farms, AI-generated pages, forums and anonymous blogs are never used.

Every entry lists, for each source: the page title, publisher, URL, the date we accessed it, and a verbatim quote containing the figure. Quotes are copied exactly as published (trimmed to 200 characters) so you can compare them against the live page.

Confidence labels: Exact — the value is fixed by law, regulation, standard or definition (a coin’s legal weight, a rulebook ball). Typical — a measured average or the middle of a published range (average body weights, an appliance model’s listed weight). Estimate — a scientific estimate where direct weighing is impossible (a T. rex, a cloud). The label is shown on every object page.

Condition matters as much as the number: adult male vs female, curb weight vs gross vehicle weight, empty vs full, water at 21 °C vs 4 °C. Each page states the condition next to the weight, and the “why weights differ” section explains the main causes of variation.

Computed values (like gallons of liquid or paper reams) follow a stated formula: weight = volume × density (or area × grammage). Each input carries its own source — the volume definition typically from NIST, the density from USGS, DOE or an equivalent authority — and the arithmetic is re-checked automatically on every build.

Rounding: exact values are shown as published. Everything else is displayed to 3 significant figures. Conversions use exact factors (1 lb = 0.45359237 kg) and are rounded only for display.

Mass vs weight: in daily English (and Chinese) we say “weight / 重量” for what a scale reads. Physically, mass is the amount of matter (kg) and weight is the force gravity exerts on it. Except for the planets tool and astronomy entries (which are masses), the numbers here are everyday weights. The planets page explains the difference in its own words.

“Last updated” dates mark when a page’s information was revised — a wording fix, a better source, a corrected conversion. A new date does not mean anyone re-weighed the object.

Found an error? Email us with the page address and a source link — corrections with verifiable sources are always welcome. HowHeavy.org is maintained by its site team; we do not invent editors, titles or credentials.