| Roof area (on plan) | — m² |
|---|---|
| Actual roof area (with pitch) | — m² |
| Area covered per sheet | — m² |
| Sheets before waste | — |
| Ridge caps | — |
| Roofing screws (approx.) | — |
This is an estimate to help you budget and order. Confirm final quantities against your actual roof before purchase — we are happy to check your figures.
Common questions about roofing quantities
How many iron sheets do I need for a 3 bedroom house in Kenya?
A typical 3 bedroom bungalow with a roof plan of about 10m x 12m and a medium pitch works out at roughly 120–130 square metres of roof. Using 3 metre box profile sheets with an effective cover of 0.80m, that is about 55 to 65 sheets once overlaps and cutting waste are allowed for. Enter your own measurements above for a figure based on your actual roof.
What is the effective cover width of a roofing sheet?
Effective cover is the width a sheet actually covers once it overlaps its neighbour — always less than the sheet you buy. Box profile typically covers 0.80m, corrugated about 0.76m, and tile profile about 0.90m. Always calculate with effective cover, never the total sheet width, or you will order short.
How much extra should I allow for waste?
Allow 5% on a simple gable roof and 10% or more where there are hips, valleys or many penetrations, because every cut leaves an offcut you cannot use. This calculator adds your chosen allowance on top of the measured area.
Why does roof pitch change the number of sheets?
The plan measurement of a building is the area on the ground. A pitched roof is longer than that along the slope, so it needs more material. A 22.5 degree pitch adds roughly 8% to the area and a 30 degree pitch roughly 15%. The calculator applies this for you.
How many ridge caps do I need?
Ridge caps run the length of the ridge and overlap each other, so each 1.8m cap covers about 1.7m. Divide the ridge length by 1.7 and round up. The calculator does this automatically once you enter the ridge length.
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