Inches to Cm Converter

Two definitions of "foot" coexisted in the United States from 1959 to 2022. The international foot (0.3048 m exactly, established by the 1959 IYPA) is the definition used by NIST, science, engineering, and consumer measurements. The U.S. survey foot (1200/3937 m ≈ 0.30480061 m) was a legacy unit retained for state-plane coordinate land surveying; it is about 2 ppm longer than the international foot — over a 100-mile baseline that drifts by ~1.06 ft. NIST and NOAA jointly announced in October 2019 that the survey foot would be deprecated, and on 31 December 2022 the deprecation took effect: from 1 January 2023 the international foot is the sole official foot in the United States for all new surveying. State plane coordinate systems are migrating to metres or to the international foot. For consumer inch-to-cm conversion the distinction is irrelevant — both definitions agree on the inch to within parts per million.

The Brannock Device — designed by Charles Brannock in Syracuse, NY (original patent filed December 1925, granted 1928 as US Patent 1,682,366; commercialised through The Brannock Device Company, founded 1927) — defines the American consumer shoe-sizing scale. US Men's size 1 corresponds to a foot length of 7⅔ in (7.667 in); each subsequent size is ⅓ in longer. The general formula is length-in-inches = (size + 22)/3 for Men's. So a US Men's size 9 measures (9+22)/3 = 10.333 in, which converts to 10.333 × 2.54 = 26.25 cm. US Women's starts at 7⅓ in (7.333 in, equivalent to Men's size 0) with the same ⅓-in step. Note that this is the foot length used by the device, not the shoe outer length — actual shoes are typically 1-1.5 cm longer than the foot itself for fit. EU sizes use the Paris point (⅔ cm = 6.667 mm per size), which is why the size numbers are larger.

They come from incompatible design conventions. ISO 216:2007 specifies the A series (A0 = 1 m² area; A4 = 210 × 297 mm exact) such that each fold preserves the same √2 aspect ratio — a property the US system lacks. US Letter (8.5 × 11 in = 21.59 × 27.94 cm) has its origin in the 19th-century US paper trade; ANSI/ASME Y14.1 codifies it as the ANSI A engineering drawing sheet size. A4 is therefore 0.59 cm narrower and 1.76 cm taller than US Letter; printing a Letter-formatted PDF at A4 size with shrink-to-fit typically scales to ~97.3% (the width-limiting ratio), leaving margin at the bottom. Most office software ships A4 default in EU locales and Letter in US locales.

Yes. The first number is the section width in millimetres (265 mm here = 26.5 cm); the second is the aspect ratio expressed as a percent (sidewall height ÷ section width × 100, so 70% of 265 mm = 185.5 mm ≈ 7.3 in sidewall height); R denotes radial construction; the trailing number is the rim diameter in inches (17 in = 43.18 cm). The split predates global metrication: wheel rims were standardised by inch fractions before tire section widths converged on millimetres, and the existing industry practice was codified rather than refactored. To estimate overall tire outside diameter from "265/70 R17": 17 in + 2 × 7.3 in = 31.6 in ≈ 80.3 cm.

US dimensional lumber is sold by nominal size — the dimensions of the rough-sawn green board before drying and surface dressing. The American Softwood Lumber Standard (Voluntary Product Standard PS 20-20, published by NIST and the American Lumber Standard Committee) defines the actual finished dimensions. A 2×4 starts at 2 × 4 in rough; after drying (which shrinks the wood) and dressing on four sides ("S4S") it ends at 1½ × 3½ in (3.81 × 8.89 cm). Similarly a 1×6 finishes at ¾ × 5½ in, a 2×6 at 1½ × 5½ in. This matters when designing a frame in metric: if you specify a 38 mm × 89 mm framing member, US carpentry will recognise that as a 2×4. The rule does not apply to plywood (sold in actual dimensions, e.g. 1220 × 2440 mm = 4 × 8 ft) or to specialty timber sold S2S (dressed two sides only).