The 2R + G walking relationship
Finished riser height R and horizontal going G describe repeated stair geometry. A widely used comfort check is 2R + G, often aimed near 600 to 630 mm. The calculator divides finished floor-to-floor height by riser count and available horizontal run by tread count, then shows the sum. It is a proportion check, not a building approval.
Worked flight: 2,720 mm high
With a finished height of 2,720 mm and 16 risers, each riser is 170 mm. A 4,050 mm run over 15 treads gives a 270 mm going. The comfort sum is 2 × 170 + 270 = 610 mm, inside the selected guide. Risers and treads are often counted differently because the upper floor or landing supplies the final tread.
Finished dimensions prevent uneven steps
Measure from finished lower floor to finished upper floor, including tile, carpet, or timber that is not yet installed. Fifteen millimetres of finish omitted at one end can make the first or last riser unsafe. Run is horizontal walking distance, not diagonal stringer length. Keep millimetres consistent: entering 2.72 into a millimetre field creates a useless result.
What the formula does not test
A good 2R + G value says nothing about headroom, width, landings, winding treads, nosings, handrails, guards, door swings, structure, accessibility, or escape rules. A spiral stair can satisfy centre-line arithmetic while being narrow at its inside edge. Local rules can specify different limits and measurement methods.
Use scenarios before cutting
Try neighbouring riser counts. Changing 16 risers to 17 makes the same height 160 mm per riser, but requires another tread or changes the going in the same footprint. Mark a full-size trial with tape and check every rise after finishes. Preserve tolerance rather than rounding a near-limit result toward acceptance.
Different from a rafter calculation
The roof tool uses rise and run for an angle and a single structural line length. This page checks repeated walking dimensions. It does not calculate stringer cuts, timber section, loads, or fixings. A diagonal hypotenuse alone misses the question that matters to a foot: each repeated horizontal going and vertical rise.
Safety limit
Stairs are fall hazards and can be part of an escape route. Final dimensions, handrails, guards, support, fire separation, and fixings need the rules that apply to the building. This local tool provides transparent geometry only; it is not a fabrication drawing or instruction to alter an existing stair.