Maker Label Studio
Construction, Trades & MEP

Roof Pitch & Rafter Calculator

Convert roof pitch, angle, percent grade, and slope factor, then calculate rafter length and ridge height from the building run.

Inputs

Use one slope input method, then enter the building span or one-sided horizontal run.

Slope

Pitch x/12, degrees, and percent grade are converted from the same rise/run ratio.
Vertical rise in the pitch ratio.
Horizontal run in the pitch ratio, commonly 12.

Building geometry

Full span uses half the span as the one-sided roof run.
Use one consistent unit for run, span, and overhang.
One-sided horizontal distance from wall plate to ridge.
Horizontal projection beyond the wall plate. Use 0 if none.

Results

Calculated from the current inputs.

Slope source Pitch: 6 / 12
Building run 10.00 ft
Overhang 0.00 ft
Pitch
6 / 12
Equivalent rise per 12 run.
Angle
26.57°
atan(rise / run), in degrees.
Percent grade
50.00%
100 x rise / run.
Slope multiplier
1.1180x
sqrt(rise^2 + run^2) / run.
Slope ratio
0.5000
Decimal rise/run ratio.
Ridge height
5.00 ft
Building run x slope ratio.
Rafter length
11.18 ft
Includes horizontal overhang converted by slope multiplier.
Rafter before overhang
11.18 ft
Building run x slope multiplier.
Reference category from the spec: Construction, Trades & MEP. Formula basis: angle = atan(rise/run), slope multiplier = sqrt(rise^2 + run^2) / run, rafter length = (building run + overhang) x slope multiplier.

Self-tests

Golden tests exercise the same pure calculation functions used by the calculator.

Self-tests have not been run.

About the Roof Pitch & Rafter Calculator

Roofers, carpenters, estimators, and designers use a roof pitch calculator to convert rise-over-run into angle, slope percentage, pitch factor, rafter length, and ridge height. Enter span, run, or pitch to check framing and material quantities before layout. It reduces mistakes when switching between x-in-12 pitch notation, degrees, and takeoff multipliers.

How it works

  1. Enter the roof rise and run, or choose a pitch such as 6 in 12.
  2. Calculate angle, slope percentage, and pitch factor.
  3. Add building span or run to estimate rafter length and ridge height.
  4. Include overhang, ridge thickness, and birdsmouth details in final layout.
  5. Check structural requirements before cutting framing members.

Frequently asked questions

What does a 6 in 12 roof pitch mean?

It means the roof rises 6 inches for every 12 inches of horizontal run. The same slope can also be expressed as an angle in degrees, a percentage, or a pitch factor for estimating.

How is rafter length calculated from pitch?

For a simple right-triangle roof, rafter length is the horizontal run multiplied by the slope factor. Final cut length may need adjustments for ridge board, overhang, seat cut, and framing details.

Is roof pitch the same as roof slope?

In common trade usage they are often used interchangeably, but pitch is frequently written as rise in 12 while slope may be expressed as a ratio, angle, or percentage.

Can pitch factor estimate roofing materials?

Yes. Multiplying horizontal roof area by pitch factor estimates sloped surface area, but waste, hips, valleys, dormers, starter courses, and product exposure must be added separately.

Does the calculator determine whether a roof is structurally adequate?

No. Structural design must consider spans, species and grade, snow, wind, dead load, connections, bracing, and locally adopted building code requirements.

References