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Roofing calculator
Enter the roof length, the rafter run from eave to ridge, and how many planes. You get the batten or rafter runs, roof area with pitch and lap allowance, ridge capping, sarking and the hours to lay it.
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Open AnyBuild freeHow the roof takeoff is worked out
Roof area is never the same as floor area, so the pitch and the laps are built into the numbers:
- Roof area is length x rafter run x number of planes, plus 10% for pitch, side laps and end laps. Measuring along the rafter rather than the plan is what keeps this honest.
- Battens (AU) are counted as rows up the rafter run at 900 mm, or 600 mm in higher wind, then run the full length of each plane.
- Rafters (US) are counted along the length at 16 or 24 in on centre per plane, and sheathing is counted in 4 x 8 sheets.
- Roof covering is priced by m² for sheeting, or by the roofing square (100 sq ft) for shingles, because that is how each is sold.
- Ridge capping comes off the ridge length with a lap allowance, and sarking or underlayment follows the roof area.
Things worth checking before you order
- Wind classification changes the fixing pattern and the batten spacing, and coastal sites also drive the material choice. Check the wind classification before you price the screws.
- Sheeting is roll-formed to length for a reason: fewer end laps, fewer leaks. Measure the run carefully before you order.
- Flashings, valleys, penetrations and gutters are their own scope. This takeoff is the roof plane, the ridge and the fixings.
- Working at height needs edge protection and the paperwork that goes with it. Allow for it in the price rather than discovering it on day one.
Common questions
How do I calculate roof area?
Measure along the rafter from eave to ridge rather than across the plan, multiply by the roof length, then by the number of planes, and add about 10% for laps. This calculator does that and adds the battens, ridge and sarking.
What is a roofing square?
100 square feet of roof area. Shingles in the US are sold and priced by the square, so the US setting works in squares while the Australian setting works in square metres.
What spacing should roof battens be at?
900 mm is common for sheet roofing in normal conditions, tightening to 600 mm in higher wind areas. Always confirm against the sheet manufacturer's span tables and your wind classification.
These figures are indicative and use sample regional trade prices, so treat them as a starting point for a quote rather than a final price. Quantities follow common practice and standard allowances; spans, footings, fixings and compliance for your specific job should be confirmed against the current standards and, where required, an engineer.
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