How to measure roof area from a plan
Quick answer
Set the scale, trace each roof plane as an area on the plan, and — because a plan shows the flat (plan) area — apply a pitch factor to get the true sloped area. Group into a condition with waste and export. Free to do in the browser.
Roof take-off from a plan has one wrinkle: a roof plan shows the flat footprint, not the actual sloped surface. Measure the plan area, then adjust for pitch to get the real quantity of covering.
This works for tiles, slates, felt, standing seam — anything measured by area.
Step by step
- 1
Set the scale
Use a ratio preset if the PDF is at true paper size, or draw over a known dimension to calibrate the sheet.
- 2
Create a roof-area condition
Make an area condition, e.g. "Roof covering", and add a waste % for cutting, laps and hips/valleys.
- 3
Trace each roof plane
With the area tool, outline each pitched plane separately (main roof, hips, dormers). Keeping planes separate makes pitch adjustment and checking easier.
- 4
Apply a pitch factor
The plan gives flat area; multiply by the pitch factor for the true sloped area (e.g. ×1.118 for 30°, ×1.414 for 45°). Note the pitch in a text label so it's auditable, or keep a separate condition per pitch.
- 5
Add flashings and edges if needed
Use linear measurements for ridge, hip, valley and eaves lengths — the perimeter of each area gives you a head start.
- 6
Export
Export a CSV of the areas (and edge lengths) for your estimate, plus an annotated PDF of the planes you measured.
Tips & gotchas
- •A roof plan shows plan area — always apply the pitch factor for the true covering quantity.
- •Keep each pitch as its own condition if the roof mixes angles.
- •Ridge, hip, valley and eaves are linear measurements — grab them from the plane perimeters.
- •Add generous waste on cut-up roofs (lots of hips and valleys).
Frequently asked questions
Does a roof plan show the real roof area?
No — it shows the flat plan (footprint) area. Multiply by the pitch factor for the angle to get the true sloped surface area you'll cover.
What's the pitch factor?
It's 1 ÷ cos(pitch angle) — roughly ×1.118 at 30° and ×1.414 at 45°. Apply it to the plan area for the sloped area.
How do I measure ridge and hip lengths?
Use linear measurements along those lines; the perimeter of each roof-plane area also gives you eaves and edge lengths.
Is it free?
Yes — area and linear measurement and export are on Solid Takeoff's free plan.
Try it on your own plan — free
Open a PDF and measure in your browser. No card, no install, no CAD. Free plan forever.