How we source and verify our data
Every number on SizeAnswer is checked against an official standard before it goes live. We use exact ISO and NIST factors, cross-check national sizing charts, and never guess. Here's exactly how.
Where our numbers come from
Conversions are only as good as their sources. We build ours from primary reference standards, not from other conversion websites:
| Domain | Primary source |
|---|---|
| Length, weight, volume | NIST & BIPM exact SI factors (1 in = 2.54 cm, 1 lb = 0.45359237 kg) |
| Paper sizes | ISO 216 (A-series) and ANSI (US Letter/Legal) |
| Ring sizes | ISO 8653 inner-circumference standard |
| Clothing & shoe sizes | EN 13402 (EU), plus national brand charts |
| Oven / gas mark | UK standard gas mark chart, cross-checked across manufacturers |
| Cooking weights | USDA ingredient density data |
How each page is checked
1. Calculate from the exact factor. We start from the defined constant (for example, 1 inch is exactly 2.54 cm), never a rounded approximation.
2. Cross-check against real charts. Sizing (shoes, clothing, bras) has no single global standard, so we compare multiple brand and national charts and publish honest ranges rather than false precision.
3. State the assumptions. Where a result depends on context — fan vs conventional oven, US vs UK fluid ounce, packed vs spooned flour — we say so on the page instead of hiding it.
4. Review before publishing. Every page is reviewed for accuracy and clarity before it goes live, and corrected promptly if a reader flags an error.
What we deliberately don't do
Spotted an error?
Accuracy matters more to us than being right. If a number looks off, tell us and we'll re-check it against the source standard and correct it if needed.
Frequently asked questions
Where does SizeAnswer get its conversion data?
From primary reference standards — NIST and BIPM for units, ISO 216 for paper, ISO 8653 for rings, EN 13402 and national brand charts for clothing and shoes, and USDA density data for cooking — not from other conversion websites.
How accurate are the conversions?
Unit conversions use exact defined factors, so they're precise. Sizing (shoes, clothing, bras) has no single world standard, so we publish honest ranges and cross-check multiple charts rather than inventing false precision.
Does advertising influence the numbers?
No. No advertiser can change a conversion, and there is no tracking. The number you see is the number the standard gives.