Roof framing spacing estimator

Rafter Spacing Calculator

Estimate rafter rows, spacing marks, total rafter length, ridge board length, blocking, waste, and rough material cost from roof length, rafter run, pitch, and on-center spacing.

Units

Roof length along ridge (ft)Horizontal rafter run (ft)Roof pitch (/12)Rafter spacing (in)Roof planes Blocking rows Waste / extras (%)Cost per rafter ($)Cost per block ($)

Rafters to buy

Rafter rows

Linear framing

Rough cost

Rafter spacing is not span design

This calculator counts layout material only. Rafter size, species, grade, snow/wind loads, span tables, ties, ridge support, connectors, and local code must be verified before building.

Android App

Need rafter spacing and roof framing takeoffs hands-free?

Use the Android app when you need voice input, offline use, material lists, or PDF export. Free, no ads, no accounts.

Get the Free App Free. Built for Android phones. Donations welcome.

Saved you a mistake? Support VibeCalc

Rafter Length Calculator

Check common rafter length from run and pitch.

Roof Pitch Calculator

Convert roof rise and run into pitch, angle, and multiplier.

On-Center Spacing Calculator

Lay out repeated framing members at any spacing.

View all

Rafter spacing formula

Rows per roof plane = roof length ÷ on-center spacing + 1

Rafters to buy = rows × roof planes × (1 + waste %)

Rafter length = √(run² + rise²), where rise = run × pitch ÷ 12

Linear footage = rafters × rafter length + ridge board + blocking

Sample takeoff

A 32 ft roof length, two planes, 12 ft run, 6/12 pitch, and 16 in spacing needs about 55 rafters with 10% waste and about 770 linear ft of framing before blocking.A 9.6 m roof length, two planes, 3.6 m run, 6/12 pitch, and 400 mm spacing needs about 55 rafters with 10% waste and about 231 m of framing before blocking.

Rafter Spacing Calculator FAQ

How does this rafter spacing calculator work?+

It multiplies measured job dimensions by the coverage, spacing, or package yield you enter, adds waste, then rounds the buy quantity up. Use the spacing required by the span table, roof assembly, and local code before relying on the count.It multiplies measured job dimensions by the coverage, spacing, or package yield you enter, adds waste, then rounds the buy quantity up. Use the spacing required by the span table, roof assembly, and local code before relying on the count.

Should I use the default waste value?+

Use the default for a quick planning estimate, then raise it for cuts, odd layouts, breakage, bad access, or product-specific loss.Use the default for a quick planning estimate, then raise it for cuts, odd layouts, breakage, bad access, or product-specific loss.

Is this a bid or code approval?+

No. It is a material planning calculator. Verify product data, local code, structural requirements, electrical requirements, and supplier packaging before ordering or building.No. It is a material planning calculator. Verify product data, local code, structural requirements, electrical requirements, and supplier packaging before ordering or building.