Sources policy

Standards and measurement bodies

• NIST - the US National Institute of Standards and Technology, for the definitions of the inch, foot, yard, pound and their metric equivalents.
• ISO and IEC - international standards for paper sizes (ISO 216), ID and bank cards (ISO/IEC 7810) and battery sizes (IEC 60086).
• ANSI and ASTM - US standards for building materials such as brick and block dimensions.

Issuers and makers

• The US Mint - official coin diameters, thicknesses and weights.
• The Bureau of Engraving and Printing - US banknote dimensions.
• Manufacturer specifications - for products with a fixed, published size, cited directly to the maker's spec sheet.

Sport and trade bodies

• League and federation rules - for regulation equipment such as a hockey puck, a soccer ball, or a golf ball, where the sport fixes the size and weight.
• Trade associations - for standardised trade items like kitchen cabinet depths.

How we cite

Every measurement page ends with a numbered sources list. Fixed figures link to the authority that sets them. Measured figures state that we measured them in house and show a photograph with a ruler in frame as the evidence. We do not cite a source we have not read, and we do not claim a standard we cannot link.