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Shed Roof Pitch Calculator

A shed roof is a single slope from a low wall to a high wall - a mono-pitch. Enter the shed width and your slope (as a 3:12 ratio, an angle, or the height difference over the run) to get the rafter length, the angle in degrees and the slope factor, with the minimum pitch your roof covering needs.

Roof slope

01. Roof type & size

Rafter run (half the span): 4.00 ft

02. Roof pitch

Slope class: conventional slope

Slope cross-section
4.47 ft2.00 ft rise4.00 ft run26.6°
Common rafter (incl. overhang)
4.81ft rafter

Roof pitch

6 : 12

Angle

26.6°

Rise

2.00 ft

Grade

50%

  • Wall to ridge4.47 ft
  • Overhang tail0.34 ft
  • Slope factor (area ×)1.1180

Multiply your roof footprint area by 1.118 to get the actual sloping area.

Guide & worked example

How this calculator works

A shed roof - also called a mono-pitch or skillion roof - is a single slope running from a low wall up to a high wall. Because only one wall carries the high side, the rafter spans the full width of the shed, so the run equals the width (unlike a gable, where the run is half the span):

run          = shed width (wall to wall)
rise         = high wall height − low wall height
slope ratio  = rise ÷ run
rafter       = sqrt(run² + rise²) = run × sqrt(1 + slope ratio²)

Pick Shed / lean-to (single slope) as the roof type above, enter the width, and set the slope however you know it: as a x:12 pitch, an angle in degrees, or the rise (the height difference between the two walls). The calculator returns the rafter length, the angle, the grade and the slope factor.

Minimum shed roof pitch by covering

CoveringMinimum pitchAngleNotes
EPDM / TPO / felt membrane~0.5 : 12~2.4°Best choice for near-flat shed roofs
Standing-seam metal1 : 12 - 2 : 124.8° - 9.5°Lowest-slope panel option
Corrugated / ribbed metal3 : 1214°Common on garden and storage sheds
Asphalt / felt shingles2 : 12 (doubled underlay)9.5°Standard application from 4 : 12

Below about 2:12 a shed roof is low slope: switch to a membrane, because shingles and most panels will let water track back under the laps.

Worked example

A 2.4 m (8 ft) wide shed at a 3:12 pitch, with a 0.3 m (1 ft) eave overhang:

  1. Run = full width = 2.4 m (single slope, so no halving).
  2. Slope ratio: 3 ÷ 12 = 0.25, so rise = 2.4 × 0.25 = 0.6 m (the high wall sits 0.6 m above the low wall).
  3. Angle: atan(0.25) = 14.0°; slope factor = √(1 + 0.25²) = 1.031.
  4. Rafter (wall to wall): 2.4 × 1.031 = 2.47 m, plus a 0.31 m overhang tail = 2.78 m to cut.

Tips

  • Set the high and low wall heights so the rise gives you a pitch that suits the covering - too shallow for shingles is the most common shed-roof mistake.
  • The run is the full width of the shed; if you halve it like a gable you will cut every rafter short.
  • Add a generous eave overhang on the low side so runoff clears the wall, and fit a gutter there.
  • Want the two-slope version, or measuring an existing roof? Use the main roof pitch calculator or the lean-to roof pitch calculator.

Frequently asked questions

01

What is the minimum pitch for a shed roof?

It depends on the covering. Asphalt shingles need at least 2:12 (9.5°) and only with a doubled underlayment below 4:12; standing-seam metal panels can go as low as 1:12 to 2:12; corrugated and ribbed metal usually want 3:12 or more; and below about 2:12 you are really into low-slope territory and should use a membrane (EPDM, TPO or torch-on felt) rather than panels or shingles. Set your slope above and the calculator labels the slope class so you can match it to the covering.

02

How do I calculate the rafter length for a shed roof?

On a single-slope shed the rafter spans the full width, wall to wall, so the run equals the shed width (not half of it). The rafter is the square root of (width squared + rise squared). Pick the "Shed / lean-to (single slope)" roof type, enter the width, and the calculator returns the rafter length plus any overhang tail.

03

What pitch should a garden shed roof be?

For a small timber shed, a 3:12 to 4:12 pitch (14° to 18°) sheds water well, suits felt shingles or metal sheet, and keeps the high wall from getting too tall. Go steeper (5:12 or more) if you want a roof that clears snow quickly or matches a house roofline; stay shallower (2:12) only if you are using a membrane or low-slope metal.

04

Is a shed roof the same as a lean-to roof?

They are both single-slope (mono-pitch) roofs, so the geometry is identical. The difference is how they are built: a freestanding shed roof sits on its own two walls, while a lean-to attaches to an existing building along its high side. If yours leans against a house or wall, use the lean-to roof pitch calculator, which works from the two wall heights.

05

How do I find the pitch if I only know the two wall heights?

Subtract the low wall height from the high wall height to get the rise, then divide by the shed width to get the slope. Choose "Rise over the run" as the pitch input, enter that height difference as the rise and the width as the run, and the calculator gives the matching x:12 pitch and angle.

06

How much overhang should a shed roof have?

A 150 to 300 mm (6 to 12 in) overhang on the eaves throws rainwater clear of the walls and protects the cladding. Enter it in the overhang field and the calculator adds its sloping length to the rafter so you cut the boards long enough. Larger overhangs look better on bigger sheds but catch more wind, so keep them modest on exposed sites.

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