Shed roof layout math

Shed Roof Pitch Calculator

Calculate shed roof pitch, roof angle, rafter length, roof surface area, plywood or OSB sheets, drip edge, and rough sheathing cost from simple rise-and-run measurements.

Roof pitch 4/12 18.4° roof angle with 8 ft 5 in rafters.
Roof shape

For a gable shed, enter the full shed width and rise from wall plate to ridge. For a lean-to, enter the horizontal run from low wall to high wall and the full rise.

Materials

Use local code and product instructions for roof framing, fasteners, underlayment, ventilation, and minimum roof slope.

How to use the shed roof pitch calculator

  1. Choose gable roof or single-slope roof.
  2. Enter the shed width or roof run and the vertical rise to the ridge or high wall.
  3. Add shed length, overhang, waste, sheet coverage, and local material prices.
  4. Use the results to compare pitch, rafter length, sheathing sheets, and trim needs before buying materials.

Pitch is shown as rise over 12 inches of run, such as 4/12. The calculator also gives the roof angle in degrees, the slope multiplier, surface area, sheathing sheet count, and a quick material estimate.

Shed roof pitch example

A 12 ft wide gable shed with a 2 ft ridge rise has a 4/12 pitch. With 6 inch overhangs and a 16 ft shed length, each rafter is about 6 ft 9.6 in before birdsmouth cuts and ridge details, and the roof surface is about 231 square feet before waste.

If you switch to a lean-to shed, the calculator treats the width field as the full horizontal run from the low wall to the high wall. That makes it useful for storage sheds, firewood shelters, chicken coop roofs, and simple backyard outbuildings.

Related shed and roof calculators

Shed foundation gravel calculator Shed ramp slope calculator Roof sheathing calculator Metal roof screw calculator

FAQ

What pitch is best for a shed roof?

There is no single best pitch. A 3/12 to 6/12 pitch is common for many sheds, but roofing material, snow, rain, looks, and headroom all matter. Follow the minimum slope for your shingles, panels, or roll roofing.

How do I convert rise and run to pitch?

Divide rise by run, then multiply by 12. For example, 24 inches of rise over 72 inches of run equals 4 inches per 12 inches, or a 4/12 pitch.

Does this include ridge board and birdsmouth cuts?

No. The rafter length is a planning length before final cuts, ridge details, seat cuts, and local framing adjustments. Buy lumber with enough extra length for your layout.

Can I use this with metal roofing?

Yes, for planning pitch, area, and trim. For fastener counts, use the related metal roof screw calculator and follow the metal panel manufacturer's installation guide.