Construction Calculator

A construction calculator works in feet-inches-sixteenths instead of decimals, which is what every tape measure on a job site reads. You can enter 10 ft 6 1/2 in, then add 4 ft 9 3/4 in, and the calculator gives you 15 ft 4 1/4 in directly. No mental conversion to decimal feet, no rounding errors, no scribbled longhand on the back of a stud.

This tool follows the layout most carpenters already know from the Construction Master Pro: dedicated feet, inch, and fraction buttons, with a yard key for concrete work and a metres key when a drawing is in mixed units. Internally everything is held as decimal feet so calculations are accurate; the display rounds to the nearest 1/16 inch because that is the smallest mark on a standard measuring tape.

Enter the pitch as a single number (8 means 8/12) plus the run, and the calculator returns the rise, the diagonal (rafter length), and the angle in degrees. A 24 ft span with a 6/12 pitch gives a rise of 6 ft 0 in, a rafter of 13 ft 5 in, and an angle of about 26.57 degrees.

Roofers in the UK and Ireland often think in degrees rather than rise-over-run, so the angle output matters. A common gotcha: pitch in the US is rise-over-12-inches, while a roof drawing from a UK architect may be expressed as a percentage or in degrees. The calculator accepts pitch as a fraction of 12 by default; convert from degrees first if your plans use that. See the [Pythagorean Theorem Calculator](/pythagorean-theorem-calculator) for the underlying maths.

Building Regs (Approved Document K) caps domestic stair risers at 220 mm and sets goings of at least 220 mm; the rule of thumb 2R + G = 600 to 620 mm gives a comfortable rhythm. Enter total rise (typically the floor-to-floor height, e.g. 8 ft 9 in) and the calculator divides it into legal risers, returns the going, the total run, and the stringer length.

If you have a fixed total run, you can work the other way: pin the run, and the calculator tells you how many treads fit and what each riser height needs to be. A staircase with a 2,650 mm total rise and 14 risers gives a riser of 189 mm and a going of about 230 mm, which is a classic pattern. Mark out the stringer with the rafter square; the diagonal output is the cut length you need.