MTMasterTool

Stair Calculator

Calculate uniform risers, treads and stair run from floor-to-floor rise.

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What this tool does

Calculate uniform risers, treads and stair run from floor-to-floor rise. The upper landing is the last riser; the stringer length is geometric, before bearing/cut allowances. Local stair code and headroom must be checked.

How to use the Stair Calculator

  1. Enter or select total rise in in.
  2. Enter or select maximum individual rise in in.
  3. Enter or select tread run in in.
  4. Read the calculated result; change any measurement to compare alternatives.

Formula

risers=ceil(rise/maxRise); treads=risers−1; run=treads×tread; stringer=sqrt(rise²+run²)
rise
Total rise (in, before metric conversion)
maxRise
Maximum individual rise (in, before metric conversion)
tread
Tread run (in, before metric conversion)

The upper landing is the last riser; the stringer length is geometric, before bearing/cut allowances. Local stair code and headroom must be checked.

Worked example

For stair calculator, the following measurements illustrate the exact method: Total rise: 108; Maximum individual rise: 7.75; Tread run: 10.

Inputs

  • Total rise108 in
  • Maximum individual rise7.75 in
  • Tread run10 in

Result

  • Number of risers14
  • Individual rise7.71 in
  • Number of treads13
  • Total run130 in
  • Stringer slope length169.01 in
  • Stair angle39.72

Results explained

Number of risers
Number of risers from the formula above. The upper landing is the last riser; the stringer length is geometric, before bearing/cut allowances. Local stair code and headroom must be checked.
Individual rise
Individual rise from the formula above, expressed in in before metric conversion. The upper landing is the last riser; the stringer length is geometric, before bearing/cut allowances. Local stair code and headroom must be checked.
Number of treads
Number of treads from the formula above. The upper landing is the last riser; the stringer length is geometric, before bearing/cut allowances. Local stair code and headroom must be checked.
Total run
Total run from the formula above, expressed in in before metric conversion. The upper landing is the last riser; the stringer length is geometric, before bearing/cut allowances. Local stair code and headroom must be checked.
Stringer slope length
Stringer slope length from the formula above, expressed in in before metric conversion. The upper landing is the last riser; the stringer length is geometric, before bearing/cut allowances. Local stair code and headroom must be checked.
Stair angle
Stair angle from the formula above. The upper landing is the last riser; the stringer length is geometric, before bearing/cut allowances. Local stair code and headroom must be checked.

Frequently asked questions

Round riser count up, divide total rise evenly, and multiply tread run by one fewer tread than risers.

Measure vertical floor-to-floor rise, allowed maximum rise and chosen tread run.

Use 5–10% for simple layouts and 10–15% for diagonal cuts or complicated outlines; the allowance is editable.

Split the outline into rectangles or triangles and calculate each section separately. Do not count overlapping sections twice.

This is a purchasing estimate, not a structural design. Confirm measurements and local requirements before buying or building.