Updated
March 27, 2026
Reviewed against the current calculator logic, structured content, and internal linking used on BuildCostLab.
Roof felt tool
Roof Felt Calculator
Estimate roof felt rolls and rough cost for sheds, garages, and outbuildings.
Methodology
Planning-first estimate
Use this calculator to build a rough material estimate, then confirm it against product coverage data, site conditions, and supplier pack sizes before you order.
Trust
How we publish
See the calculator methodology and editorial policy for the standards behind these pages.
Assumptions
Roofing estimates rely on covered area, lap or overlap allowances, and the fact that roof shape and pitch often increase the real material take-off above a simple plan area.
Common mistakes
Common issues include ignoring overlap, failing to allow for cuts at edges and ridges, and treating every roof as if it behaves like a simple rectangle.
Best use cases
Best for sheds, garages, simple roofs, and early roofing material checks where the buyer needs a fast but practical order estimate.
How to get a better estimate
Check whether the product is sold by effective coverage after laps or by nominal pack size, because that changes the buying count immediately.
Before you buy
Roofing jobs rarely reward under-ordering. A small overage is usually cheaper than the disruption caused by a short finish course or delayed extra delivery.
UK and US note
Terms vary between roofing systems and markets, but overlaps, pitch, edge waste, and actual covered area remain the critical estimate drivers.
Final buying check
Before placing an order, compare product coverage, pack size, delivery cost, and whether buying one extra unit is safer than risking a shortfall.
Explore this topic cluster
Open the full Roofing Estimating hub to move from quick estimate to deeper guidance.
How do I use the roof felt calculator?
Enter the job dimensions, choose a realistic waste setting, and use the roof felt calculator to get a planning quantity before checking product-specific coverage or pack rules.
What most affects the roof felt calculator result?
Common issues include ignoring overlap, failing to allow for cuts at edges and ridges, and treating every roof as if it behaves like a simple rectangle.
Should I round the result up?
Roofing jobs rarely reward under-ordering. A small overage is usually cheaper than the disruption caused by a short finish course or delayed extra delivery.