About
Who writes these calculators and how the numbers are checked.
About DATUM
Who made these, why they exist, and what they are not.
Who. DATUM is written by a practising architect in New York. Every calculator here is one I use, or one I got tired of not being able to trust. No employer, client or project is represented on this site — the work here is mine and separate from it.
Why. Search for any construction calculator and you get a dozen near-identical pages. They give you a number to seven decimal places, cite nothing, and stop. That is fine until the number matters. A stair can be arithmetically perfect and still fail inspection. A concrete order can be correct and still leave you short at the far end of a pour. Those are the cases this site is built for.
How the numbers are checked. Every constant on this site names its source. Bag yields cite the manufacturer's technical data sheet number. Code limits cite the section number. Unit conversions use exact legal definitions rather than rounded factors — 1 pyeong is 400/121 m², 1 ft² is 0.09290304 m². If a number appears here, you can go and check it against the source.
How they are maintained. Building codes get amended and manufacturers change their products. A calculator running on a superseded code is worse than no calculator, so the constants get re-checked against their sources on a schedule rather than set once and forgotten.
Your inputs stay in your browser. Every calculator here runs entirely as JavaScript on the page you are looking at. Nothing you type is transmitted, logged or stored anywhere. There is no account, no form and no database behind any of it.
What this is not. These are design aids, not compliance certifications and not professional advice. Building codes are amended by state and local jurisdiction; confirm the adopted edition and any local amendment with the authority having jurisdiction before relying on anything here. Manufacturer figures vary by product — check the bag, the box or the data sheet you actually have. For anything that carries real consequence, have it reviewed by the licensed professional responsible for the work.