Shed Roof Pitch
4/12
Pitch Conversions
Rafter & Dimensions
Roofing Material Guidance
Any roofing material works. Asphalt shingles, metal panels, or corrugated steel are all good options.
Common Shed Roof Pitches
| Pitch | Angle | Factor | Notes |
|---|---|---|---|
| 1/12 | 4.8° | 1.003 | Nearly flat - minimum for shingles |
| 2/12 | 9.5° | 1.014 | Low slope - metal or roll roofing |
| 3/12 | 14.0° | 1.031 | Minimum for standard shingles |
| 4/12 | 18.4° | 1.054 | Common shed roof pitch |
| 5/12 | 22.6° | 1.083 | Good water runoff |
| 6/12 | 26.6° | 1.118 | Standard residential pitch |
| 8/12 | 33.7° | 1.202 | Steep shed - snow country |
| 10/12 | 39.8° | 1.302 | Very steep - decorative sheds |
| 12/12 | 45.0° | 1.414 | 45 degrees |
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Last updated: 2026-03-27
How Shed Roof Pitch Works
I've framed dozens of shed roofs over the years, from 8x10 storage sheds to 16x24 workshops. The pitch is the single decision that affects everything else: rafter length, wall heights, roofing material options, and how well the roof handles rain and snow. Get it wrong and you are re-framing walls or fighting leaks.
A shed roof (also called a mono-slope or lean-to roof) is the simplest roof to build. One high wall, one low wall, rafters running from one to the other at a consistent slope. No ridge board to cut, no opposing rafters to align. That simplicity is why it is the go-to for outbuildings, workshops, and lean-to additions.
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Understanding pitch, angle, and slope factor
Pitch is expressed as rise over 12 inches of horizontal run. A 4/12 pitch means the roof rises 4 inches for every 12 inches it travels horizontally. That same slope can also be described as an 18.4-degree angle or a 33.3% grade. Builders use pitch. Engineers use degrees. Surveyors use percent. This calculator converts between all three instantly.
The slope factor is what turns horizontal measurements into actual rafter length. It is calculated as the square root of (1 + (rise/12) squared). For a 4/12 pitch, the slope factor is 1.054, meaning every foot of horizontal run becomes 1.054 feet of rafter. Seems like a small difference until you are cutting 20 rafters and each one needs to be right.
Common shed roof pitches and when to use them
| Pitch | Angle | Rise per 12 ft Width | Best Use |
|---|---|---|---|
| 2/12 | 9.5° | 2 ft | Metal roof lean-tos, carports |
| 3/12 | 14.0° | 3 ft | Minimum for shingles, flat-look sheds |
| 4/12 | 18.4° | 4 ft | Most common - good drainage, reasonable walls |
| 5/12 | 22.6° | 5 ft | Better for rain, slightly taller high wall |
| 6/12 | 26.6° | 6 ft | Snow country, matches house roof pitch |
| 8/12 | 33.7° | 8 ft | Heavy snow areas, loft storage |
How to pick the right pitch for your shed
Start with your roofing material. If you want asphalt shingles, you need at least 3/12. Metal panels work down to 1/12 or 2/12 depending on the profile and seam type. That minimum sets your floor.
Next, think about wall height. A 12-foot-wide shed at 4/12 adds 4 feet of rise. If your low wall is 7 feet, the high wall hits 11 feet. That is fine for most sheds. But bump the pitch to 8/12 on the same 12-foot width and your high wall is 15 feet tall. Now you might need a building permit, taller studs, and the shed starts looking odd next to the house.
- Storage sheds (8-12 ft wide): 3/12 to 4/12 keeps walls manageable and material costs low.
- Workshops (12-20 ft wide): 4/12 to 5/12 gives good headroom on the high side for overhead storage.
- Lean-to additions: Match the existing house roof pitch so the lines look intentional.
- Snow country: 6/12 or steeper. Snow loads on low-pitch roofs can be 3-4x what they are on steep roofs.
Cutting rafters for a shed roof
A shed rafter has three cuts: a plumb cut at the high wall, a birds mouth notch where it sits on each wall plate, and a tail cut at the overhang. The plumb cut angle matches your pitch. On a 4/12 roof, set your speed square to 4 and mark the plumb line.
Here is the formula that matters: rafter length = (shed width + overhang) x slope factor. For a 12-foot shed with a 12-inch overhang at 4/12 pitch: (12 + 1) x 1.054 = 13.7 feet. Buy 14-foot lumber. You will trim the extra for the tail cut.
I've seen guys try to skip the math and just hold a board up to mark the cut. Works on a doghouse. Does not work on a 16-foot shed where being off by half an inch at the wall means you are off by 2 inches at the far end. Do the math once, cut a pattern rafter, test the fit, then cut the rest.
Quick pitch reference formulas
- Pitch to angle: angle = arctan(rise / 12) in degrees
- Slope factor: sqrt(1 + (rise / 12)²)
- Rafter length: (width + overhang) x slope factor
- Wall height difference: width x (rise / 12)
- Roof area per foot of length: (width + overhang) x slope factor
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How to Use This Calculator
Choose your input method
Select pitch (rise per 12 inches of run), total rise and run measurements, or roof angle in degrees. If you know the pitch from your plans, that is the fastest option. If you are measuring an existing shed, use rise and run.
Enter your shed width
Measure the horizontal distance from the low wall to the high wall in feet. This is the run of the roof, not the slope distance. A typical storage shed runs 8 to 16 feet wide. Larger workshop sheds might be 20 to 24 feet.
Set the eave overhang
Enter how far the roof extends past the wall in inches. Standard shed overhang is 6 to 12 inches. More overhang protects the walls from rain but adds rafter length. Every extra inch of overhang adds material and cost.
Read your results
The calculator shows your pitch in all formats (rise/run, degrees, slope factor, percentage), rafter length including overhang, total roof rise, and the wall height difference between the high and low sides. Use these numbers to cut rafters and frame walls.
Frequently Asked Questions
What is the best roof pitch for a shed?
A 4/12 pitch is the most common shed roof slope. It gives enough angle for water runoff with asphalt shingles while keeping the high wall at a reasonable height. For a 12-foot-wide shed, a 4/12 pitch adds 4 feet of rise, so if your low wall is 7 feet, your high wall is 11 feet. That is plenty of headroom without looking awkward.
What is the minimum roof pitch for a shed?
The absolute minimum depends on your roofing material. Metal panels can go as low as 1/12 to 2/12. Asphalt shingles need at least 3/12, and even then you should use ice and water shield underneath. Below 2/12 you are in flat-roof territory and need membrane, built-up, or EPDM rubber roofing. Going too flat invites leaks, standing water, and snow load problems.
How do I calculate shed rafter length?
Multiply the horizontal run by the slope factor. For a 12-foot-wide shed with a 4/12 pitch: slope factor = sqrt(1 + (4/12)²) = 1.054. Add your overhang (say 1 foot) to the run, making it 13 feet. Rafter length = 13 x 1.054 = 13.7 feet. Always add 6 inches for the birds mouth cut and tail cut. Buy 14-foot lumber.
How do I convert roof pitch to degrees?
Use the formula: angle = arctan(rise / run). For a 4/12 pitch: arctan(4/12) = arctan(0.333) = 18.4 degrees. Common conversions: 3/12 = 14.0°, 4/12 = 18.4°, 5/12 = 22.6°, 6/12 = 26.6°, 8/12 = 33.7°, 12/12 = 45.0°. Most speed squares have both pitch and degree markings.
How much taller is the high wall on a shed roof?
The difference equals your shed width multiplied by the pitch ratio. A 12-foot-wide shed at 4/12 pitch rises 4 feet across the span, so the high wall is 4 feet taller than the low wall. If the low wall is 7 feet, the high wall is 11 feet. For a 10-foot-wide shed at the same pitch, the difference is 3 feet 4 inches.
Should I use a single slope or gable roof on a shed?
A single-slope (shed roof) is simpler and cheaper to build. One ridge beam, one set of rafters, no ridge cuts. It works great for lean-tos, storage sheds, and workshops under 20 feet wide. A gable roof looks more traditional and spreads snow load evenly, but requires ridge framing and twice as many rafter cuts. For sheds under 16 feet wide, a single slope is the way to go.
What roofing material works best on a low-pitch shed?
At 3/12 or steeper, standard asphalt shingles work fine. Between 2/12 and 3/12, use metal panels or roll roofing with sealed seams. Below 2/12, you need a membrane system like EPDM rubber, TPO, or modified bitumen. Metal standing seam is the best all-around choice for low-pitch sheds because it handles water, snow, and looks good doing it.
How do I measure an existing shed roof pitch?
The easiest method: hold a 2-foot level against the underside of a rafter with one end touching the rafter. Level it, then measure the vertical distance from the other end of the level down to the rafter. That measurement in inches is your pitch per 12 inches. So if you measure 4 inches of drop in 12 inches of horizontal run, you have a 4/12 pitch. A speed square also works if you can reach the roof edge.
Related Roof Calculators
- Roof Pitch Calculator - Convert pitch, angle, and slope for any roof type
- Roof Sheathing Calculator - Calculate OSB or plywood sheets needed by roof size
- Rafter Calculator - Full rafter dimensions with ridge, birdsmouth, and tail cuts
- Shingle Calculator - Bundles and squares for asphalt shingle roofing
- Roof Area Calculator - Total roof area from footprint and pitch
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