Changing language restores only pinned measurements.
One-slope roof pitch calculator
RiseRunRafterAngle (°)Slope (%)US pitch (X/12)Vertical height.Horizontal distance, not full span.Sloping length, excluding overhang.From 0° to less than 90°.Rise per 100 horizontal units.Rise per 12 horizontal units; enter X only.Check the selected measurements and enter numeric values.Choose a supported calculator mode.Choose one of the listed pairs of known values.Use only the selected known values.Enter a number with a decimal point, such as 2.5. Commas and fractions are not supported.This value is outside the supported numeric range. Enter a smaller finite number.Enter zero or a positive number. Rise cannot be negative.Run must be greater than zero. A vertical slope has no horizontal run.Geometric rafter length must be greater than zero.Enter an angle from 0° up to (but not including) 90°.Choose a supported length unit.The geometric rafter cannot be shorter than the rise or run. Check both measurements.These measurements describe different slopes. Check both known values.These values are too extreme to represent reliably. Use less extreme measurements.Choose between 0 and 4 decimal places.RiseRunRafter lengthAngle (°)Slope (%)US pitch (X/12)Grade ratio (rise : run)Complementary angle1 in X (run per rise)PitchLengthsConvertFrom rise and run.Any two values — find the missing length.Degrees, percent and X/12, side by side.CalculatedProportions onlyAwaiting measurementsCheck your inputsDone. Lengths describe one triangle.Proportions only — no lengths yet. Add a length in Lengths to get dimensions.Enter both values, or try an example below.These values don’t determine a unique size. Pick a pair with a run or rafter length.Flat (no rise)1 in {value}Unavailable in {unit}Unknown (a length is required){field} unite.g. {value}Unit unchanged.Some source units stayed unchanged. Correct incomplete or invalid values before converting them.Results copied.Copy unavailable. Select and copy the visible results manually.CalcSlope — roof pitch & slopeUS pitch = rise per 12 horizontal run. Rafter excludes overhang; no structural sizing.Rise {rise}; run {run}; rafter {rafter}; angle {angleDeg}.Proportions only — dimensions unknown. Angle {angleDeg}; slope {slopePercent}; US pitch {pitchX12}.Enter values to draw your slope. Rise is vertical, run is horizontal, rafter is the sloping side.Proportions only · dimensions unknownTo scale · values on the labelsIllustration onlyAngle {value}{status}. Angle {angleDeg}, slope {slopePercent}, US pitch {pitchX12}.PinPinnedPin {field} valueUnpin {field} valueMeasurement pinned on this device.Measurement unpinned.Enter a valid measurement before pinning.Invalid measurement unpinned; its saved value was removed.Device storage is unavailable. Pins work on this page only; use browser site-data settings to remove any earlier saved values.Saved measurements cleared. Current inputs remain.This example would change a pinned measurement. Unpin it or choose another example.
Enter values to draw your slope. Rise is vertical, run is horizontal, rafter is the sloping side.
Results
Results
One-Slope Calculation
Angle (°)
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Slope (%)
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US pitch (X/12)
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Rafter length
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Rise
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Run
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Complementary angle
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Grade ratio (rise : run)
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1 in X (run per rise)
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Enter valid lengths to print a calculation report.
How roof pitch works
A roof pitch describes how steeply a roof rises over a horizontal distance. This tool connects rise and run to degrees, percent and US X/12 notation.
Choose and enter your measurements
Identify both ends of one straight slope. Use their height difference and horizontal projection from the same reference, on an existing drawing or at accessible measurement points.
Use Pitch for rise and run. Use Lengths when you know a rafter length or an angle plus a length. Each field has its own unit, so convert feet and inches through the selectors rather than entering a mixed expression.
Read X/12 alongside degrees and percent. Changing the display unit preserves the physical measurement; changing precision only rounds the displayed answer. Changing a mode or known-value selection starts fresh.
House outline with a 3–4–5 triangle at the eave. Run is level, rise is the height difference. Walls, door and window are illustrative only.
Rise: 3.00 m · Run: 4.00 m · Rafter: 5.00 m
Rise, run and rafter: three different lengths
Rise
Vertical difference between the ends of one slope, not the whole building height.
Horizontal run
The level projection of that slope, not its sloping length. Half a building span applies only to known symmetric geometry; the calculator never halves your input.
Rafter length
The straight sloping side, excluding overhang, cuts and construction allowances.
Pitch, percent and angle
Degrees measure the angle above horizontal. Percent means rise per 100 horizontal units; US X/12 uses 12. X/12 is a convention, not a building rule.
For the same 3–4–5 triangle, degrees, percent and US pitch describe one inclination. X/12 uses twelve horizontal units; it is not a building rule.
Use the same length unit for h (rise) and d (horizontal run). Let l be the geometric rafter and θ the angle above horizontal. The tool converts mixed input units before solving.
Slope (%) = 100 × h ÷ d
US pitch X/12: X = 12 × h ÷ d
θ = arctan(h ÷ d) × 180 ÷ π
l² = h² + d²
Slope (%) = 100 × tan(θ × π ÷ 180)
Degrees and percent are not interchangeable: 45° is 100%, while 30° is about 57.74%. Inclination alone determines proportions, not the size of a roof. A known length sets the scale. Two inclination inputs only check agreement.
Three worked examples
These examples use the same calculation engine as the tool. Values shown here are rounded to two decimal places; choose four decimal places in the calculator for a closer view.
A 6/12 pitch in inches
Known values: Rise: 6 in · Run: 12 in
Rise: 6.00 in · Run: 12.00 in · Rafter length: 13.42 in · Angle (°): 26.57° · Slope (%): 50.00% · US pitch (X/12): 6.00/12
A metric 3–4–5 triangle
Known values: Rise: 3 m · Run: 4 m
Rise: 3.00 m · Run: 4.00 m · Rafter length: 5.00 m · Angle (°): 36.87° · Slope (%): 75.00% · US pitch (X/12): 9.00/12
A 30° slope with a 4 m run
Known values: Run: 4 m · Angle (°): 30°
Rise: 2.31 m · Run: 4.00 m · Rafter length: 4.62 m · Angle (°): 30.00° · Slope (%): 57.74% · US pitch (X/12): 6.93/12
Roof pitch questions
Does this work for shed roofs?
Yes, for the geometric triangle of one straight slope. Enter the actual horizontal distance between its endpoints and their height difference. No dedicated roof-form drawing, material takeoff or structural design is produced.
Is run the same as building width?
Only if that width is the horizontal projection of the particular slope you are measuring. For two roof sides, measure each slope separately unless the geometry is known to be symmetric.
Why no lengths in Compare mode?
An angle, percentage or X/12 pitch describes a proportion. Many differently sized triangles share that proportion. Use Lengths with a known length to get dimensions.
What does 1 in X mean?
It gives one unit of vertical rise for X units of horizontal run. It is a length ratio, not a percentage. With zero rise the slope is flat and this reciprocal has no finite value.
Can this choose my roofing material?
The result describes geometry only. It does not specify a minimum pitch, loading, member sizes or a compliant roof covering. Those choices require the relevant project information and product guidance.
