What does the rafter span calculator include?

Check rafter span assumptions and calculate rafter length from run, pitch, overhang, and ridge allowance. The default estimate adds 10% waste, which you can edit.

Should I round the result up?

Yes. Order whole bags or cartons, and order bulk material in the supplier's available increment after adding 5% to 10% for site loss.

Can I enter metric measurements?

Yes. The unit switch accepts metric measurements without creating a separate URL.

Is this result a code approval?

No. The displayed table and edition are a planning reference. Local code and a licensed professional govern structural work.

Rafter Span

Calculated result / live

12.3 ft rafter

Cut each rafter to about 12.30 ft before allowing for birdsmouth and ridge cuts.

10.00 ft horizontal run, 6.0 in rise per 12 in, and 1.00 ft overhang. Geometry is not a structural span approval.

Input panel

Project measurements

Horizontal runftRise per 12in / 12 inOverhangftRafter countraftersWaste%

Secondary quantities
Horizontal run	10.00 ft
Pitch factor	1.118
Rafter length	12.30 ft

Calculation trace

Formula with your numbers

(10.00 + 1.00) ft × √(12² + 6.0²) ÷ 12 = 12.30 ft

Take to supplier

Materials list

2 rafters at 12.30 ft
10% cut allowance
Verify species, grade, snow load, and local code before framing

12.3 ft rafter

01

What this rafter span calculator calculates

A 10 ft run with a 6 in rise per 12 in and a 1 ft overhang produces a 12.30 ft sloped length.

Formula

Horizontal length × √(12² + rise²) ÷ 12 = sloped length.

Worked example

(10 + 1) × √(12² + 6²) ÷ 12 = 12.30 ft before birdsmouth, ridge, and waste cuts.

Ordering decision

Species, grade, snow load, bearing, heel height, and local code decide whether a rafter can span the building.

The page cites the applicable Uzi Tools reference table beside the calculator. Product labels, current editions, local code, and a licensed professional govern structural, electrical, and life-safety work.

02

How to use it

Enter the measured dimensions and keep the displayed units beside each field.
Review the rafter length from run and pitch result and the substituted formula before ordering.
Adjust waste for the layout, cut pattern, product package, and site conditions.
Copy or print the material list, then verify the cited product data and local requirements.

03

Rafter length from run and pitch

This rafter page calculates sloped rafter length from horizontal run, pitch rise, and overhang. It states the geometry separately from the structural span question.

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Limits and professional review

Measurements, product yield, waste, moisture, and site conditions can change the order quantity. Local code and a licensed professional govern structural and electrical work.

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Data sources

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Related calculations

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Same-project tools

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Rafter Span Calculator