Roof calculator: area, pitch, tile and panel metering
Free roof calculator: enter plan size, eaves and pitch % to get net roof area (m²), ridge/gutter lengths, tile / ridge-tile counts or sandwich panel–sheet metering. No sign-up.
How are roof area and covering metered?
A pitched roof surface is larger than the plan area. This tool adds eaves to building length and width, derives rise and rafter length from pitch %, then multiplies by two faces (gable) or one (mono) for net m². It then estimates tile or panel order quantities.
Steps
Choose roof type: gable (two faces) or mono-pitch.
Choose covering: tile or metal / sandwich panel.
Enter length, width, eaves per side and pitch percent.
Set waste % (often 8–12%). For tiles enter pcs/m²; for panels enter effective width and spare panels.
Read net area, order area, ridge/gutter and material results.
Formulas
Eaves length / width
Length + 2 × eaves · Width + 2 × eaves
Horizontal run
Gable: eaves width ÷ 2 · Mono: eaves width
Rise
Run × pitch % ÷ 100
Rafter length
√(run² + rise²)
Net roof area
Rafter × eaves length × faces (2 or 1)
Tile / panel
Tile: ⌈order area × pcs/m²⌉ · Panel: ⌈eaves length ÷ panel width⌉ × faces + extras
Pitch % ≠ degrees: 100% pitch = 45°. Angle = arctan(pitch%/100). Order area = net × (1 + waste%/100). In panel mode, % waste is not auto-applied to panel count — use spare panels for overlaps.
Sample results
Default sample: 12 × 10 m building, 50 cm eaves, 30% pitch, gable.
Net roof area
≈ 149.3 m²
Eaves 13 × 11 m; half-width 5.5 m; rise 1.65 m; rafter ≈ 5.74 m × 13 × 2.
Ridge / gutter
13 m · 26 m
Ridge ≈ eaves length; gutter ≈ 2 × eaves length (gable).
Tiles (10% waste, 12/m²)
≈ 1,971 pcs
Order area (~164.2 m²) × 12, rounded up. Ridge tiles separately.
Pitch angle ↔ percent ↔ area factor
Reference values from the same right triangle. Factor ≈ 1 / cos(angle).
| Angle | Pitch % | Area factor |
|---|---|---|
| 10° | 17.6% | 1.015 |
| 15° | 26.8% | 1.035 |
| 20° | 36.4% | 1.064 |
| 25° | 46.6% | 1.103 |
| 30° | 57.7% | 1.155 |
| 35° | 70% | 1.221 |
| 40° | 83.9% | 1.305 |
| 45° | 100% | 1.414 |
Suggested pitches by covering
Climate, manufacturer sheets and waterproofing set the pitch. Ranges below are guidance.
| Covering | Common pitch | Note |
|---|---|---|
| Clay / concrete tile | 22°–60° (40%–175%) | Underlayment required at low pitch |
| Metal / trapezoidal sheet | 7°–45° (12%–100%) | Increase overlap at low pitch |
| Sandwich panel | Per manufacturer | Effective cover width varies by model |
| Membrane / bituminous | 2°–10° (3.5%–18%) | Terraces and low-pitch roofs |
Practical tips
- “30% pitch” is not “30° pitch”; enter percent in the tool.
- On a gable, run is half the eaves width — the tool splits it.
- Don’t forget eaves: 50 cm grows plan area on a 10×12 m building.
- Take pcs/m² from the tile catalogue — it varies by model.
- On hip roofs raise waste and meter ridges/valleys separately.
Application note
Result is geometric preliminary metering. Final order follows the roof plan, module, overlaps and site cuts.
Related calculators
Continue with structure and metering:
Frequently asked questions
How is roof area calculated?
Add eaves to plan size. Rise comes from pitch %. Rafter = √(run²+rise²). Net area = rafter × eaves length × faces (2 on a gable).
Pitch percent or degrees?
This tool wants percent. 100% pitch = 45°. If you know degrees: percent ≈ tan(angle)×100.
Gable vs mono-pitch?
Gable has two faces and a ridge; run is half eaves width. Mono has one face; run is the full eaves width.
Why add eaves on both sides?
Eaves project on length and width. Formula: length+2×eaves and width+2×eaves.
How are tile counts found?
Order area × catalogue pcs/m², rounded up. Ridge tiles = ridge length × pcs per metre.
Why isn’t panel waste automatic?
Overlaps and cuts vary by supplier. Use effective cover width and spare panels; m² waste is for membrane / general order area.
How to read ridge and gutter?
Gable: ridge ≈ eaves length; gutter ≈ 2 × eaves length. Mono: ridge 0; gutter ≈ eaves length.
Is a hip roof exact?
No. Hips, valleys and cuts must be measured on the plan; raise waste.
Does this do structural / snow load?
No. Geometric covering metering only. Structure follows the project and manufacturer sheets.