Pergola and patio-cover slope estimator

Pergola Roof Slope Calculator

Convert pergola run and target pitch into height drop, slope angle, rafter length, panel length, and rough material cost. Useful for patio covers, lean-to pergolas, and low-slope rain-shedding layouts.

Units

Roof run (ft)Target pitch (/12)Extra overhang allowance (ft)Rafters or panels Waste / trim allowance (%)Cost per rafter/panel ($)

Height drop

Slope angle

Panel length

Rough cost

Low-slope covers need product checks

This calculator gives geometry only. Roofing panels, polycarbonate sheets, drainage, snow load, attachment, flashing, minimum slope, permits, and local code can change the final pergola roof layout.

Android App

Need pergola roof slope and rafter checks 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

Roof Pitch Calculator

Convert roof rise and run into slope angle and multiplier.

Lean-To Rafter Calculator

Check single-slope rafter geometry for shed-style roofs.

Metal Roof Length Calculator

Estimate sloped panel length and count for metal roofing.

View all

Pergola roof slope formula

Height drop = run × pitch ÷ 12

Slope angle = arctan(height drop ÷ run)

Rafter length = √(run² + height drop²)

Panel length = rafter length + overhang allowance

Sample takeoff

A 12 ft pergola roof run at 2/12 pitch drops 24 in, has about a 9.5° slope angle, and needs about 12.7 ft panels with the default overhang allowance.A 3.6 m pergola roof run at 2/12 pitch drops 600 mm, has about a 9.5° slope angle, and needs about 3.8 m panels with the default overhang allowance.

Pergola Roof Slope Calculator FAQ

How does this pergola roof slope calculator work?+

It multiplies measured job dimensions by the coverage, spacing, or package yield you enter, adds waste, then rounds the buy quantity up. Check the roofing product for the minimum pitch it allows before using a low-slope result.It multiplies measured job dimensions by the coverage, spacing, or package yield you enter, adds waste, then rounds the buy quantity up. Check the roofing product for the minimum pitch it allows before using a low-slope result.

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.