About these tools and how they are checked

What this site is

CheckConvert is a small set of free unit, number and time converters. Each page does one job, opens with a worked example and explains in plain words how the answer is reached, including the awkward cases. The site will be paid for by advertising; no ads are shown yet. There is no sign-up, and nothing you type leaves your browser (see privacy).

Operated by Longitude Press (sole trader), ABN 38 842 876 454, NSW.

How the conversions are done

• A time with no am or pm is read as 24-hour. 12 AM is 0000 and 12 PM is 1200.
• Decimal hours are minutes divided by 60; the main answer is rounded to two places and a four-place figure is shown beside it.
• Every unit factor is an exact legal definition (NIST Handbook 44 and Special Publication 811, the BIPM SI Brochure, the UK Weights and Measures Act 1985): 1 inch is 2.54 cm, 1 pound is 0.45359237 kg, 1 US gallon is 3.785411784 L and 1 imperial gallon 4.54609 L.
• Units that differ by country (gallons, pints, fluid ounces, cups, tablespoons, tons, horsepower) are listed as separate units, never mixed.
• The unit maths lives in cv.js.
• Roman numerals follow the standard form from 1 to 3,999 (only IV, IX, XL, XC, CD and CM take away); from 4,000 to 3,999,999 a bar over letters multiplies them by 1,000.
• Hex, binary and octal conversions use exact whole numbers of any size (BigInt), so nothing is rounded. Negative numbers keep a minus sign; two's complement is shown separately.
• Numbers in words use the short scale (1 billion = 1,000,000,000). UK and Australian style adds "and" before the tens and ones; Indian style groups in lakhs and crores.
• The number tools use a third script, nb.js.
• All of it lives in one small script, tt.js, which you are welcome to read.

How the tools are checked

Before the site is published, an automated check opens every page in a real browser (Chromium) and types in questions with known answers. The published pages have to give those answers. Some of them:

• 7:45 is 7.75 decimal hours, and 7.75 hours is 7:45:00.
• 1430 is 2:30 PM; 12:15 AM is 0015; 2400 is read as midnight, 0000.
• 70 kg is 154.3236 lb; 30 cm is 11.811 in; 1 mi is exactly 1.609344 km; 20 °C is 68 °F and −40 °C is −40 °F.
• 70 kg is 11 st 0.3 lb; 170 cm is 5 ft 6.9 in; 250 mL is 8.4535 US fl oz and 8.7988 imperial fl oz; 100 kW is 134.1022 hp.
• 1994 is MCMXCIV and 3,999 is MMMCMXCIX; IIII, IC and VV are refused; every number from 1 to 3,999,999 turns into a numeral and back to itself in the unit tests.
• 255 is FF in hex, 11111111 in binary and 377 in octal; 2⁶⁴ is 10000000000000000 in hex; -1 is FF in 8-bit two's complement.
• 2,505 is two thousand five hundred five (US) and two thousand five hundred and five (UK); 12,34,567 is twelve lakh thirty-four thousand five hundred sixty-seven.

The same check confirms that no page reports a script error, that every page fits a 360 pixel wide phone screen without sideways scrolling, and that every internal link leads somewhere. The functions in tt.js are also tested on their own, outside the browser.

What has not been checked

• The automated check runs in Chromium only. Other browsers and screen readers have not been tested.

Found a mistake?

Email [email protected] with the page, what you typed and what you expected. Confirmed errors are fixed and added to the check.