Measurement & Conversion Calculators

Google answers "inches to millimetres" with a widget above every result, and there is no point competing with that. What it does not answer is "what is 0.4375 on a tape measure" — and that is the question people are actually asking when they reach for a converter mid-job.

Every tool here exists because the conversion is specific to a trade: decimal to tape fractions, board feet, roof pitch to slope factor, drawing scale to real dimensions, taper angle to a saw setting. Those are the ones that get worked out wrong on a Sunday afternoon.

Squaring and cubing. There are nine square feet in a square yard and twenty-seven cubic feet in a cubic yard, not three of either — because area squares the linear conversion and volume cubes it. Using three gives an answer three or nine times wrong, and it is the single most common mistake in material estimating.

The other is pound-inches against pound-feet. They differ by a factor of twelve, and applying twelve times the intended torque strips almost any fastener. Small-fastener specs are given in pound-inches precisely because the numbers stay readable, which is exactly what makes them easy to misread.

The same slope appears as a percentage grade on a site drawing, as degrees on a protractor, as a ratio in an accessibility spec, and as fall per foot on a drainage detail. They all describe one thing, and converting between them by eye is unreliable — percentage and degrees are close below ten per cent and separate sharply above twenty.

The same problem shows up on tapered cuts, where the angle from vertical and the included angle at the base are complements of each other. One is what a saw is set to; the other is what a protractor reads. Confirming which your tool wants before cutting saves the piece.