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.

Results

Risers
14
Treads
13
Actual riser
7.714in
Total run
130.00in
Stringer length
169.01in

Straight-line length of the carriage.

Stair angle
39.7°
2R + T (Blondel)
25.43in

Recommended gear

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. 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). 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.

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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