唐字寫如兩呎四吋，英文two feet and four inches。減筆用單撇′代呎，雙撇″代吋，所以就寫成2′−4″、2′ 4″或者2′4″。國際上，亦會以ft.代呎。
- See, for example, Report on the Comparisons of the Parliamentary Copies of the Imperial Standards with the Imperial Standard Yard and the Imperial Standard Pound and with each other during the Years 1947 to 1948 (H.M.S.O., London, 1950). Report on the Comparisons of the Parliamentary Copies of the Imperial Standards with each other during the Year 1957 (H.M.S.O., London, 1958).
- Bigg, P. H.; Anderton, Pamela (1964), "The United Kingdom standards of the yard in terms of the metre", Br. J. Appl. Phys., 15: 291–300, doi:10.1088/0508-3443/15/3/308.
- "On what basis is one inch exactly equal to 25.4 mm? Has the imperial inch been adjusted to give this exact fit and if so when?". National Physical Laboratory. 喺2010-07-13搵到.