Woodworking & Construction Calculators

Carpentry & framing

Stair Rise and Run Calculator (Riser, Tread, Stringer)

Enter the floor-to-floor rise and a comfortable target riser. The tool rounds to a whole number of risers, sets treads to risers minus one, and gives stringer length from Pythagoras.

Inputs

Units
in

Floor-to-floor height, including finish floors.

in

Comfortable step height. Many codes cap this near 7¾ in (197 mm).

in

Run of each tread, nosing excluded from the stringer triangle.

Terms of Service

Results

Please tick the box above to display the Result.

Calculation method

A flight between two floors has one more riser than treads. The calculator rounds total rise ÷ target riser to a whole number of risers, then actual riser = total rise ÷ that count. Stringer length is the hypotenuse of total rise and total run. Stair angle is the pitch of the line through the nosings, arctan(actual riser ÷ tread depth). Blondel’s 2R + T is a comfort check, not a code.

Exact formula

risers = round(totalRise / targetRiser). actualRiser = totalRise / risers. treads = risers − 1. totalRun = treads × treadDepth. stringer = √(rise² + run²). stair angle = arctan(actualRiser / treadDepth). Blondel = 2R + T, often near 24–25 in (610–635 mm).

Imperial and metric stairs

US codes speak in inches. European drawings often use millimetres. The unit toggle converts the same flight without changing the number of risers.

Frequently asked questions

Why is there one more riser than treads?

You step up onto the landing. Fourteen risers and thirteen treads is the usual floor-to-floor pattern.

What riser height is comfortable?

7–7¾ in (178–197 mm) is common. Always check the local maximum. The riser count is rounded to the nearest whole number, so the actual riser can land slightly above your target; if you typed the code maximum and the actual riser comes out above it, lower the target a little until the count goes up by one.

Does this include nosing?

No. Tread depth here is the stringer run. Nosing adds to the walking surface, not to Pythagoras on the carriage.

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