Roof Tile Calculator (UK)
Last updated: 12 August 2026
Work out how many roof tiles or slates you need, along with the battens and underlay to fix them. Enter the roof dimensions and choose your covering.
How the calculation works
Roof area = eaves length × rafter length × number of sides. If you only know the span and pitch, use the roof pitch calculator first to get the true rafter length — using the flat plan dimension underestimates the area by 15% or more.
Tiles per square metre varies hugely by type, so we use your selection rather than a single average. Battens are calculated from the batten gauge, and underlay includes 15% for laps at horizontal joints and verges.
Tiles per square metre by type
| Covering | Per m² | Typical gauge |
|---|---|---|
| Large interlocking concrete | ~10 | 345mm |
| Interlocking pantile | ~13 | 300mm |
| Plain tile (double lap) | ~60 | 100mm |
| Slate 500 × 250mm | ~21 | ~200mm |
| Slate 400 × 250mm | ~26 | ~150mm |
These are guide figures. Every manufacturer publishes an exact gauge and coverage for their product at your specific roof pitch — always confirm against that before ordering, because the minimum lap increases as the pitch gets shallower.
Battens and fixing
BS 5534 requires graded battens, normally 25 × 50mm for rafters at 600mm centres. Every tile at eaves, ridge, verge and in the two courses at the edges must be mechanically fixed, and in exposed areas the whole roof may need clipping. Wind uplift calculations are the roofer job, not a rule of thumb.
Frequently asked questions
How many roof tiles do I need per square metre?
It depends on the tile. Large interlocking concrete tiles need about 10 per square metre, interlocking pantiles about 13, plain tiles around 60, and natural slate 21 to 26 depending on size and lap.
How do I calculate roof area?
Multiply the length along the eaves by the rafter length from eaves to ridge, then by the number of roof sides. Do not use the flat footprint — a 30 degree pitch makes the actual roof area about 15% larger than the plan area.
How many slates per square metre?
About 21 per square metre for 500 x 250mm slates and 26 for 400 x 250mm, at standard laps. Shallower pitches need a bigger lap, which increases the number per square metre.
What size battens do I need for roof tiles?
25 x 50mm graded battens are standard for rafters at 600mm centres under BS 5534. The batten gauge — the spacing between them — comes from the tile manufacturer figures for your roof pitch.
How much felt do I need for a roof?
Roof area plus about 15% for horizontal laps and verge overhangs. Underlay usually comes in 1m x 50m rolls, so a 60 square metre roof needs two rolls.
Related calculators
Roof Pitch Calculator
Pitch in degrees, rise:run ratio and rafter length.
Loft Insulation Calculator
Rolls of mineral wool for 270mm loft insulation.
Day Rate & Quote Calculator
Price a job from day rate, materials and markup — VAT included.
Estimates are for guidance only. Material dimensions, densities and coverage vary by supplier — always confirm quantities before ordering, and consult a qualified professional for structural work.