Roof Pitch Calculator
LIVE RESULTStandard run = 12 in
Your Results
PITCH · ANGLE · SLOPEConventional / standard slope
Drag the orange apex to change both rise and run, or the blue handles to adjust one at a time. The boxes above stay in sync.
Single Slope · Mono-Pitch
Lean-To & Shed Roof Pitch Calculator
A lean-to, shed, pergola or extension roof is a single slope, so its pitch is simply the rise across the run. Enter the height difference (rise) and the horizontal depth (run) to get the pitch, angle and slope — then check it against the minimum recommended falls below.
- Works for lean-to, shed, mono-pitch, pergola & extension roofs
- Rise = height drop across the roof; run = horizontal depth
- Get pitch ratio, angle in degrees and slope %
- Minimum-fall guidance so water drains properly
How a Lean-To Roof Pitch Is Calculated
A lean-to (also called a mono-pitch or single-slope roof) has just one sloping surface. The rise is the difference in height between the high wall and the low wall; the run is the horizontal depth the roof spans. The pitch is rise over run, exactly like a standard roof:
pitch = rise ÷ run · angle° = arctan(rise ÷ run)
Enter those two numbers above to get the pitch as an X:12 ratio, the angle in degrees and the slope percentage. To find the rise from a target angle, see the rise & height calculator. For dead-flat roofs, use the flat roof fall calculator.
Minimum Pitch for a Lean-To or Shed Roof
Too shallow and water pools; the safe minimum depends on the covering. These are common guide figures — always confirm against the manufacturer’s specification and local codes.
| Covering | Typical minimum pitch |
|---|---|
| Fibreglass / GRP | 10° (about 2:12) |
| Single-ply membrane (EPDM) | 1–5° (with falls) |
| Corrugated metal sheet | 5–10° |
| Polycarbonate (pergola/canopy) | 5° minimum |
| Standard shingles | 2:12 min (special underlay below 4:12) |
Frequently Asked Questions
What is the minimum pitch for a lean-to roof?
It depends on the covering. Fibreglass is usually about 10 degrees, corrugated metal around 5 to 10 degrees, and membrane systems can go very low provided proper falls are built in.
How do I calculate a shed roof slope?
Divide the height difference between the tall and short walls by the horizontal depth of the roof. That ratio is the slope; its arctangent is the angle in degrees.
Is a lean-to roof the same as a mono-pitch roof?
Yes. Lean-to, mono-pitch and single-slope all describe a roof with one sloping plane, often built against a taller wall.
More Roof Pitch Calculators
Purpose-built tools for every roofing measurement — pick the one that matches your job.
Roof Pitch Multiplier
Slope-factor calculator & full multiplier chart
Roof Pitch to Degrees
Convert pitch to degrees and back, with a chart
Roof Pitch Chart
Every pitch in degrees, slope % and multiplier
Roof Rise & Height
Find roof rise and ridge height from pitch and span
Flat Roof Fall
Fall in mm per metre, ratio and angle
Roof Pitch Calculator
The main rise-over-run tool with live diagram