Stair Builder Calculator: Full Build Workflow from Rise to Cut List

Step 1: establish total rise

Total rise is the exact vertical distance between the two finished floor levels the stair connects, measured with a spirit level and tape rather than assumed from a drawing, because finished floor build-ups (screed, tile, flooring) often differ from the plans by 10-20mm (0.5-0.75in). Every other number in the build flows from this measurement, so get it from the actual site, not the architect's section drawing.

Step 2: fix the riser count and height

Divide total rise by a target riser height to get a first-pass step count, then round to the nearest whole number and divide back to get the exact riser height every step will use. UK Approved Document K limits riser height to a maximum of 220mm (8.66in) on a private stair, with 170-190mm (6.7-7.5in) being typical comfortable practice. US IRC R311.7.5 caps riser height at 7.75in (196mm) with a maximum variance of 3/8in (9.5mm) between any two risers in the same flight — a tolerance the calculator enforces automatically by using one exact riser height throughout.

For a total rise of 2.75m (9ft 0.25in), targeting roughly 180mm (7.1in) risers: 2750 / 180 = 15.3, round to 15 steps, then 2750 / 15 = 183.3mm (7.2in) exact riser height. Every one of the 15 risers on this flight is built to exactly 183.3mm, which is what keeps the flight compliant and, more practically, keeps every step feeling identical underfoot.

Step 3: choose the going

Going is set using the standard comfort formula: 2 x riser height + going should fall between about 550-700mm (21.5-27.5in), with 600-650mm (24-25.5in) considered the most comfortable middle ground. With a 183.3mm riser, a going of about 250-270mm (10-10.6in) lands the formula in the ideal range. UK Part K also sets a minimum going of 220mm (8.66in) on a private stair, while US IRC R311.7.4 requires a minimum going (tread depth) of 10in (254mm), which is generally the binding constraint on US builds and pushes the going choice up towards 10-11in almost automatically.

Step 4: work out stringer length

The stringer is the sloped structural board the treads and risers are fixed to, and its length is the hypotenuse of the triangle formed by total rise and total going, exactly as with handrail: stringer length = square root of (total rise squared + total going squared). For the 15-step example with a going of 260mm, total going is 14 x 260mm = 3640mm (going is only counted between step nosings, so an n-step flight has n-1 goings). Total rise is 2750mm. Stringer length = sqrt(2750^2 + 3640^2) = sqrt(7,562,500 + 13,249,600) = sqrt(20,812,100) = 4562mm (14ft 11.6in).

Always add a horizontal offcut allowance of at least one tread depth at both the top and bottom of the stringer board so there is enough timber to cut the top birdsmouth and the bottom kick plate without running off the end of the board. On the example above, order stringer stock at 4562mm plus roughly 500-600mm (20-24in) allowance, so a 5.2m (17ft) board with some margin to spare, or the nearest standard US lumber length above 15ft — typically a 16ft or 20ft 2x12.

UK vs US stringer material conventions

In the US, stringers are almost always cut from 2x12 dimensional lumber (nominal 2in x 12in, actual 38 x 286mm) because a 12in-wide board gives enough depth to cut the step notches while leaving at least the code-minimum 3.5in (89mm) of solid timber below the deepest notch point, per IRC R311.7.5.1. A 2x10 (actual 38 x 235mm) is sometimes used on shorter-going stairs but leaves less margin and is checked case by case. In the UK, stringers are typically cut from 32-38mm (1.25-1.5in) thick softwood or engineered board, 225-300mm (9-12in) deep, following the same principle of leaving enough solid material below the deepest cut.

Step 5: the full cut list

With riser height, going and stringer length fixed, the calculator produces a complete cut list: the number of stringers (2 for a stair up to about 900mm/36in wide, 3 for anything wider or with open risers), the tread boards cut to the finished width plus nosing overhand, the riser boards if the design is closed-riser, and any newel posts or ledger boards needed to fix the top of the stringers to the upper floor structure.

• Stringers: 2-3 boards at the calculated length plus offcut allowance.
• Treads: one per step, cut to finished width plus 20-25mm (0.75-1in) nosing overhang at the front.
• Risers (closed-riser only): one per step, cut to riser height plus any rebate allowance into the tread above and below.
• Ledger board: fixed to the upper floor structure to carry the top of the stringers, sized to match the stringer thickness.
• Kicker plate: fixed to the floor or landing at the base of the stringers to stop lateral movement.
• Fixings: construction screws or joist hangers rated for stair loading, plus PL premium or equivalent adhesive on interior builds.

Cost overview: materials for a 15-step interior flight

A straightforward closed-riser interior staircase of 15 steps, built from PSE softwood in the UK, typically runs £600-£1,200 in structural timber, treads and risers before finishing, or £1,800-£3,500 fully fitted with balustrade by a joiner. The same flight in the US, built from 2x12 stringers with pine or oak treads, typically runs $700-$1,400 in materials, or $2,200-$4,200 installed by a stair-building contractor including railing.

1. Measure total rise on site with a level and tape.
2. Divide by a target riser height, round the step count, recompute the exact riser height.
3. Set going using the 2R+G comfort rule and any code minimum going.
4. Calculate stringer length as the hypotenuse of rise and total going.
5. Generate the cut list: stringers, treads, risers, ledger and kicker allowances.

Whatever you decide, get the numbers first: the stair runner calculator doubles as a stair runner length calculator, adding nosing wrap, landings, winders, pattern repeat and waste so you order the right length the first time.