Rafter Length Calculator

Enter span, pitch, ridge thickness and overhang for simple common-rafter geometry, then review cut-angle context and a proportional roof preview.

Building span (ft)

Roof pitch (rise per 12)

Ridge board thickness (in)

Horizontal overhang (in)

—Rafter run

—Roof rise

—Wall-to-ridge length

—With overhang

—Simple common-rafter geometry; cut details and structural sizing are not included.

Use project drawings and local requirements for actual framing. This calculator does not determine member size, load capacity, birdsmouth cuts, connections, or code compliance.

Cut-angle & board-length context

Use the same span/pitch inputs to expose tape-friendly lengths, roof angle and simple common-rafter cut geometry.

—Wall-to-ridge

—With tail

—Plumb-cut angle

—Roof / seat angle

Geometry only. Birdsmouth depth, member size, load capacity, connections and local code are project-specific.

Construction Calculator Feet & Inches Square Footage Linear Feet Cut List Rafter Concrete

Stock & spacing planner

Turn one rafter length into an estimating plan with stock length, rafter count and total linear footage.

Cut-list evidence

Building length (ft)

On-center spacing (in)

Stock allowance (in)

Use the tool above, then refresh this audit.

Audit uses the visible inputs plus the assumptions shown here.

Field measurement & procurement tolerance audit

Rebuild the visible project math independently, then perturb the field measurements to expose a min/base/max envelope before cutting or ordering. This is a planning cross-check, not structural engineering, code approval, or supplier certification.

Measurement toleranceTolerance basisInterpretation

Refresh the field audit after entering project measurements above.

Browser-local planning cross-check. Verify final dimensions on site before cutting or ordering.

Construction field-work cluster

Carry measurement uncertainty into the material decision

Use the exact calculator first, then stress-test realistic field measurement and rounding tolerance before a cut or purchase. Keep structural design, code approval and supplier specifications outside the browser estimate.

Start: Construction Calculator Check Area

All 30 construction tools

RafterSpan, pitch, board length and field tolerance Roof PitchRise/run, angle, factor and measurement sensitivity BrickOpenings, waste, modules and order sensitivity Cubic YardsVolume, waste, delivery and tolerance envelope Feet & InchesTape arithmetic, fraction rounding and tolerance Cut ListCut lengths, kerf, stock and tolerance GravelDepth, density, tonnage and order sensitivity StairsRise/run geometry and field-measurement sensitivity

Practical guide and verification

Geometry is not structural design

A rafter calculator can relate run, rise, pitch and geometric length, but it does not determine whether a rafter size, species, grade, spacing or connection is structurally adequate for a building.

Use consistent reference points

Decide whether measurements refer to horizontal run, common-rafter line, ridge centerline, wall plate, overhang or birdsmouth location. Mixing reference points is a common reason field measurements disagree with a geometric result.

Common mistake

Do not add an overhang or ridge allowance twice. Separate the basic roof triangle from construction-specific adjustments so each addition has a clear physical meaning.

Planning notes

Start with the measurement this calculator asks for, then use related length, area/volume, roof, stair, material, waste, or cut-planning tools only when the job needs them. Inputs and results stay in the browser.