Quick reference: a 6:12 pitch = about 26.6° = 50% slope = 1.118× pitch factor. That means a simple 2,000 sq ft horizontal roof plan becomes about 2,236 sq ft of sloped roof surface before irregular geometry or separate overhang adjustments.
Free roofing calculator • 4 input methods
Roof Pitch Calculator: Degrees, Slope, Rafter Length & Roof Area
Convert rise/run, degrees or percent slope into roof pitch. Or enter simple gable-roof dimensions to estimate pitch factor, rafter length, roof surface area and roofing squares in one workflow.
Calculate your roof pitch
Choose the measurement you already know. The same result is converted into pitch, degrees, percent slope and area factor.
Planning geometry only. Verify measurements and roof planes before ordering material. Do not access a steep, wet, damaged or otherwise unsafe roof to improve an online estimate.
Roof pitch calculator formulas
Roof pitch describes how much a roof rises vertically for a given horizontal run. In U.S. residential roofing, a pitch such as 6:12 means the roof rises 6 units for every 12 horizontal units. The calculator converts the same slope into several formats because drawings, contractors, product documents and homeowners may use different notation.
| Result | Formula | 6:12 example |
|---|---|---|
| Pitch ratio | Rise ÷ Run, normalized to 12 | 6:12 |
| Percent slope | (Rise ÷ Run) × 100 | 50% |
| Angle | arctan(Rise ÷ Run) | 26.6° |
| Pitch factor | √(1 + slope ratio²) | 1.118× |
Roof pitch to degrees, percent slope and multiplier table
| Pitch | Degrees | Percent slope | Pitch factor |
|---|---|---|---|
| 1:12 | 4.8° | 8.3% | 1.003 |
| 2:12 | 9.5° | 16.7% | 1.014 |
| 3:12 | 14.0° | 25.0% | 1.031 |
| 4:12 | 18.4° | 33.3% | 1.054 |
| 5:12 | 22.6° | 41.7% | 1.083 |
| 6:12 | 26.6° | 50.0% | 1.118 |
| 7:12 | 30.3° | 58.3% | 1.158 |
| 8:12 | 33.7° | 66.7% | 1.202 |
| 9:12 | 36.9° | 75.0% | 1.250 |
| 10:12 | 39.8° | 83.3% | 1.302 |
| 11:12 | 42.5° | 91.7% | 1.357 |
| 12:12 | 45.0° | 100.0% | 1.414 |
| 14:12 | 49.4° | 116.7% | 1.537 |
| 16:12 | 53.1° | 133.3% | 1.667 |
| 18:12 | 56.3° | 150.0% | 1.803 |
How to calculate roof area from pitch
If you know the horizontal roof-plan area for a simple roof, multiply it by the pitch factor to estimate sloped surface area. A 2,000 sq ft horizontal plan at 6:12 uses the 1.118 factor:
2,000 × 1.118 ≈ 2,236 sq ft of sloped roof surface.
That is approximately 22.36 roofing squares before a material-order allowance. This is why house living area should not automatically be used as roof area: story count, overhangs, garages, porches and roof geometry can make the two numbers very different.
Simple gable roof area from building dimensions
The fourth calculator mode estimates a simple symmetrical gable roof using building width, building length, pitch and optional overhangs. It first calculates half the horizontal span from ridge to eave, applies the pitch factor to get approximate slope length, then multiplies the slope length by roof length for both roof planes.
This is useful for a straightforward detached garage, shed or simple house roof. It is not a replacement for a roof-plane takeoff on hips, valleys, dormers, L-shaped buildings, additions or intersecting roofs.
Roof pitch and rafter length
For a simple straight slope, approximate rafter or slope length is the horizontal ridge-to-eave span multiplied by the pitch factor. For example, a 14 ft horizontal span at 6:12 is about 15.65 ft before ridge-board, birdsmouth, tail and construction-detail adjustments. Do not use this planning result as a cut length for structural framing.
Degrees to roof pitch
If you have an angle from a digital level or drawing, the calculator converts degrees back to pitch by taking the tangent of the angle. For example, 26.6° is approximately a 6:12 roof, while 45° is a 12:12 roof. Use the Roof angle in degrees mode rather than manually converting.
Percent slope to roof pitch
Percent slope equals rise divided by run multiplied by 100. A 33.3% slope is about 4:12; 50% is 6:12; 100% is 12:12. This conversion is helpful when a survey, civil drawing or other document reports slope as a percentage instead of X:12.
Why roof pitch affects replacement cost
Pitch can affect a roof replacement budget in two different ways. First, steeper pitch creates more roof surface over the same horizontal plan, which increases material quantity. Second, access, staging and fall-protection requirements can change labor. The exact labor premium varies by contractor and project, so the calculator keeps the geometry separate from cost assumptions.
After confirming roof surface area, use the Roofing Square Calculator to plan squares and bundles, then use the Roof Replacement Cost Calculator to model material, tear-off, decking, state and contingency assumptions.
Roof pitch, roofing squares and shingle quantity
Roof pitch is only the first quantity step. Once you know approximate roof surface area:
- Divide roof surface area by 100 to get base roofing squares.
- Add a justified material allowance based on geometry and the selected product.
- Use the exact product's package coverage to convert squares into bundles or panels.
- Keep starter, ridge/hip cap, underlayment, flashing and other accessories separate unless the product system says otherwise.
The roofing square and shingle bundle calculator performs that next conversion and includes common 1,000–5,000 sq ft examples.
How to measure roof pitch without unsafe roof access
Do not climb onto a roof merely to get a better online estimate. Depending on the building, pitch may be obtained from plans, an accessible attic rafter, a professional measurement report or a safe ground-based method. If a roof is steep, wet, damaged, icy or storm-affected, leave roof access to qualified professionals. OSHA identifies falls as a major construction hazard and publishes fall-prevention resources.
Common roof pitch mistakes
- Using house square footage as roof surface: living area is not automatically the roof plan or sloped roof area.
- Applying pitch twice: if an aerial or contractor report already gives sloped roof surface, do not multiply by a pitch factor again.
- Ignoring overhangs: eaves and rake overhangs can add measurable area.
- Assuming one pitch covers every plane: additions and complex roofs can have several slopes.
- Using rafter planning length as a structural cut length: real framing details require more information.
- Ordering directly from a geometry estimate: product coverage and roof layout determine the final material order.
Roof pitch action plan: turn the number into a roof decision
- Calculate: convert your known measurement into pitch, degrees, slope and pitch factor above.
- Verify area: add a horizontal footprint or simple gable dimensions, or use a reliable roof measurement report for complex geometry.
- Convert quantity: open the Roofing Square Calculator and record base squares plus your material allowance.
- Build the budget: run the Roof Replacement Cost Calculator using actual roof surface, not interior living area.
- Compare contractor measurements: if two bids use different square counts, ask each roofer to show net roof area, waste, overhangs and excluded sections before comparing price.
Your output should be: Pitch ____:12 • Angle ____° • Roof surface ____ sq ft • Base roofing squares ____ • Contractor measurement A ____ • B ____ • C ____.
Roof pitch FAQ
What angle is a 4:12 roof pitch?
Approximately 18.4°, with a 33.3% slope and a pitch factor of about 1.054.
What angle is a 6:12 roof pitch?
Approximately 26.6°, with a 50% slope and a pitch factor of about 1.118.
What angle is an 8:12 roof pitch?
Approximately 33.7°, with a 66.7% slope and a pitch factor of about 1.202.
What angle is a 12:12 roof pitch?
45°, with a 100% slope and a pitch factor of about 1.414.
What is roof pitch factor?
Pitch factor, sometimes called slope or area multiplier, converts horizontal run or plan area into approximate sloped length or area for simple geometry.
Can this calculator give exact roof area?
It can estimate simple geometry. Complex roofs should be split into individual planes or measured with plans, field measurement or a professional roof report.
What pitch is a 30-degree roof?
The tangent of 30° is about 0.577. Multiplied by 12, that is about 6.9:12, commonly rounded for discussion to roughly 7:12.
What pitch is a 45-degree roof?
45° equals a 12:12 pitch because rise equals horizontal run.
Can I use roof pitch to estimate shingle bundles?
Only after you also know roof surface area. Use this page to estimate surface, then the Roofing Square Calculator to convert area into squares and product-specific bundle quantity.
Related roofing tools
- Roofing Square & Shingle Bundle Calculator
- Roof Replacement Cost Calculator
- Roof Decking Replacement Cost Calculator
- How to Measure Roof Pitch
- Roof Replacement Planning for a 2,000 Sq Ft House
Method reviewed September 24, 2026 • Geometry formulas are shown above • HomeCostEngine methodology