Use this Shed Roof Pitch Calculator to plan a simple single-slope roof from horizontal run and either roof pitch or vertical rise. Calculate angle, slope factor and straight-line roof geometry with optional overhangs.
Enter shed roof geometry
Choose whether you know the pitch or the vertical rise across the horizontal run.
Your shed roof layout
Review pitch, rise, angle and straight-line roof geometry across the run and optional overhangs.
Transparent calculation
How shed roof geometry is calculated
The run and rise form a right triangle. In pitch mode the vertical rise is generated from the x:12 pitch ratio; in rise mode the pitch is calculated from the entered rise and run.
run × pitch ÷ 12(rise ÷ run) × 12atan(rise ÷ run)√(1 + (rise ÷ run)²)run × slope factor(run + overhangs) × factorImportant: the result is geometric length along one simple roof line. Finished member length and roof-system details can differ because of cuts, bearing, ridge/wall conditions, fascia and structural requirements.
Step by step
How to use the Shed Roof Calculator
Measure the horizontal run between the wall/reference points of the single-slope roof. Then choose whether you know the pitch or the vertical rise across that run. Optional overhangs are entered horizontally so the calculator can convert them to sloped geometry.
- Enter horizontal run. Do not enter the existing sloped roof length.
- Choose pitch or rise. Pitch mode is useful when the roof slope is specified; rise mode is useful when wall-height difference is known.
- Add overhangs if needed. Enter low-side and high-side horizontal extensions separately.
- Calculate. Review pitch, rise, angle, slope factor and straight-line lengths.
- Apply structural/cut details separately. The tool does not size or detail actual rafters.
Read your result
What each shed roof result means
Roof pitch
The vertical rise for every 12 units of horizontal run.
Vertical rise
The height difference created across the entered horizontal run.
Roof angle
The angle of the roof plane above horizontal.
Slope factor
The multiplier that converts horizontal distance into straight-line sloped distance.
Sloped span
The straight roof-line distance between the selected run reference points before overhangs.
Total sloped geometry
The sloped span plus the geometry created by the entered horizontal overhangs.
Worked example
Example: 12 ft run at a 3:12 pitch
A 12 ft horizontal run at a 3:12 pitch rises 3 ft. The roof angle is about 14.0°, the slope factor is about 1.031, and the straight sloped span is roughly 12.37 ft. Adding a 1 ft horizontal low-side overhang increases the total horizontal roof line to 13 ft before applying the same slope factor.
12 × 3/12 = 3 ftatan(3 ÷ 12) ≈ 14.0°√(1 + .25²) ≈ 1.03112 × 1.031 ≈ 12.37 ftMeasurement guidance
Shed roof planning tips
- Use horizontal run between consistent reference points.
- If you know high and low wall elevations, their difference can be entered as vertical rise.
- Check roofing-material minimum/maximum slope requirements separately.
- Do not assume geometric sloped length is a finished rafter cut length.
- Confirm drainage, flashing, structural loading and connection details for the actual project.
Know the limits
Assumptions and limitations
This calculator models one straight, uniform single-slope roof plane. It does not determine wall framing, rafter/joist size, structural span, snow/wind loads, connections, bearing, waterproofing details, drainage capacity or suitability of any roof covering for the selected slope.
Overhang inputs are horizontal distances. Actual fascia, tail, seat/plumb cuts and support details can change physical member dimensions.
Common questions
Shed Roof Calculator FAQ
What is a shed roof?
A shed or lean-to roof is a single sloped roof plane rather than two slopes meeting at a ridge.
Can I calculate pitch from wall-height difference?
Yes. Use Rise & Run mode and enter the vertical difference as rise and the horizontal distance as run.
Does the result include overhang?
The total sloped geometry includes any horizontal low-side and high-side overhangs you enter.
Does this size the rafters?
No. Structural member sizing depends on loads, spans, species/grade, spacing, connections and adopted requirements.
Can I use a very low roof pitch?
The geometry calculator can model low slopes, but roof-covering and drainage requirements must be checked separately for the actual product and project.
Can I use metric units?
Yes. Switch to Metric and enter horizontal run, rise and overhangs in millimeters.
Keep planning
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Sources & methodology
How this page is checked
The calculator uses right-triangle geometry and exposes every slope assumption. Structural, waterproofing and material suitability decisions remain outside the calculation.