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Calcimator

Precast Stair Design Calculator

Calculate precast stair dimensions, riser/tread count, stringer length, and weight from floor-to-floor height per IBC code.

Inputs

ft
in
in
in
pcf

Results

Total risers

22

Risers per flight11
Actual riser height6.55 in
Treads per flight10
Run per flight9.17 ft
Stringer length10.96 ft
Stair slope angle33.2°
Estimated weight9,043 lbs
Plan length12.83 ft
Comfort index (2R+T)24.09 in
Total Treads20
Comfort OkYes
Riser OkYes
Tread OkYes
Width OkYes
How to Use This Calculator
  1. Enter the floor-to-floor height in ft and the clear stair width in inches (IBC minimum 44 in for >50 occupants).
  2. Set the maximum riser height in inches (IBC max 7 in) and minimum tread depth (IBC min 11 in).
  3. Enter the number of flights per floor (2 for a standard switchback stair).
  4. Read Total Risers and Actual Riser Height (in) to verify equal divisions and IBC compliance.
  5. Check Comfort Index (2R+T) — the ideal range is 24–25.5 inches for user comfort.
  6. Use Estimated Weight (lbs) and Stringer Length (ft) for crane picks and precast mold planning.

How the result changes with Floor-to-floor height

Floor-to-floor heightTotal risers
8.316
1222
1526
1934

What each input means

Floor-to-floor height
Vertical distance between finished floor levels.
Stair width
Clear width of stair (IBC min 44 in for >50 occupants).
Max riser height
Maximum riser height (IBC max 7 in).
Min tread depth
Minimum tread depth (IBC min 11 in).
Flights per floor
Number of flights per floor (2 = typical switchback).
Concrete unit weight
Concrete density (NW ~150 pcf, LW ~115 pcf).

What each result means

Total risers
Total number of risers from floor to floor.
Risers per flight
Number of risers in each flight.
Actual riser height
Exact riser height for equal division.
Treads per flight
Number of treads per flight (risers minus 1).
Run per flight
Horizontal run of one flight.
Stringer length
Length along the stringer (for precast mold).
Stair slope angle
Angle of the stair from horizontal.
Estimated weight
Approximate weight of all precast stair sections per floor.
Plan length
Total horizontal footprint of the stair.
Comfort index (2R+T)
Stair comfort ratio — ideal range is 24-25.5 inches.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Floor-to-floor height = 12, Stair width = 44, Max riser height = 7, Min tread depth = 11 = 6 input(s) provided
  2. Calculate Total risers
    Total risers
    22 = 22
  3. Calculate Risers per flight
    Risers per flight
    11 = 11
  4. Calculate Actual riser height
    Actual riser height = floorToFloorInches / totalRisers
    6.55 = 6.55

Engine last updated .

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