Stair Calculator

Calculate equal stair risers, treads, total run and geometric stringer diagonal from total rise, maximum riser height and tread depth. Calculate it clearly with Figur.

Split total rise into equal risers and solve the diagonal

Use inches throughout. Risers = round up(total rise ÷ maximum riser height), at least 1. Equal riser height = total rise ÷ risers. Treads = risers − 1, assuming the upper landing is the final walking surface. Total run = treads × tread depth. Stringer diagonal = √(total rise² + total run²); divide by 12 for feet. The diagonal is geometry, not a stock-board length or cutting template.

Method and assumptions

Risers = max(1, round up(total rise ÷ max riser)); riser height = total rise ÷ risers; treads = risers − 1; run = treads × tread depth; diagonal = √(rise² + run²).

  • One straight flight with equal risers is modeled; the upper landing replaces the last tread.
  • Total rise, maximum riser and tread depth are in inches. Displayed dimensions have up to two decimals; calculations use unrounded values.
  • Maximum riser and tread depth are user inputs, not a determination of local code limits. No material count or waste allowance is calculated.
  • Stringer count, stock width/length, notches, bearing, nosing, finished-floor offsets, intermediate landings, headroom and handrail design are excluded.

Planning takeoff, not a binding bid, structural design or engineering advice. Confirm field measurements, product coverage, installation requirements and supplier quantities before buying.

Sources and references

The result uses your inputs and the tool's documented assumptions; it does not fetch current prices, rates or products.

Worked example

A stair flight rises 45 inches, with maximum riser height 7.75 inches and tread depth 10.5 inches.

45 ÷ 7.75 = 5.806…, rounded up to 6 risers. Each riser is 45 ÷ 6 = 7.50 in. There are 5 treads and 5 × 10.5 = 52.50 in of run. √(45² + 52.5²) = 69.15 in diagonal, or 5.76 ft.

Frequently asked questions

Why is there one fewer tread than risers?

The upper landing is treated as the last walking surface. Different landing arrangements require their own layout.

Can I buy or cut a stringer at the displayed diagonal?

Not from this figure alone. It is the rise/run hypotenuse, excluding stock allowances, bearing details and notch layout.

Does it certify code compliance?

No. Confirm riser, tread, headroom, landing and handrail requirements locally before choosing dimensions or cutting material.

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