Figure

Roof and stairs

Common rafters

Find rafter length and cuts from pitch and span or measured rise and run.1

A common rafter follows the roof’s rise and horizontal run. Half of the full span supplies the run only for a symmetric layout. The geometric length excludes project-specific overhang and ridge adjustments.

From pitch and full span

For a symmetric roof, divide full span by two to get run. Length excludes overhang and ridge adjustment.

Start a new calculation

Use 2nd if a unit is above its button.

  1. Start fresh

    Press Clear entry, then Clear entry.

  2. Press the keys

    Press Select length units.

Open Roof

Skip if Roof is already open. Skip Close if no mode is open.

  1. Press Close calculation mode, then Open Roof.

Enter and calculate

  1. Pitch per foot

    Press 7, then inches, then Store pitch 1.

  2. Full span

    Press 14, then feet, then 4, then inches.

  3. Halve the span and assign Run

    Press Divide, then 2, then Equals, then Store run.

  4. Read the rafter length

    Press Select Common group.

Results in orderPress = to continue

  1. Length8 feet 3 and 9/16 inches
  2. Plumb cut30.25644°
  3. Level cut59.74356°
  4. Pitch per foot7 inches
  5. Grade58.33333
  6. Slope0.5833333
  7. Run7 feet 2 inches
  8. Rise4 feet 2 and 3/16 inches
  9. Length again8 feet 3 and 9/16 inches

Keep in mind

Use half-span only when the ridge divides this roof's span equally. Add or subtract project-specific overhang and ridge allowances separately.

Pitch unknown: rise and run known

Use measured vertical rise and horizontal run.

Start a new calculation

Use 2nd if a unit is above its button.

  1. Start fresh

    Press Clear entry, then Clear entry.

  2. Press the keys

    Press Select length units.

Open Roof

Skip if Roof is already open. Skip Close if no mode is open.

  1. Press Close calculation mode, then Open Roof.

Enter and calculate

  1. Rise

    Press 6, then feet, then 11, then inches, then 1, then Fraction, then 2, then Store rise.

  2. Run

    Press 14, then feet, then 6, then inches, then Store run.

  3. Press the keys

    Press Select Common group.

Results in orderPress = to continue

  1. Example result16 feet 1 inch
  2. Plumb cut25.63565°
  3. Level cut64.36435°
  4. Pitch per foot5 and 3/4 inches

Keep in mind

Rounded measurements retain their underlying value unless the workflow explicitly rounds a stair step.

Display assumptions

  1. Fraction precision: 1/16″; Fraction format: Simplified; Angle decimal places: Variable. ↩

Keep the guide beside your calculation.

These examples are built into Figure. Open Help while you calculate, then return to the same guide and reading position.

See Help in Figure →