Roof tile calculator

Plain tiles need about 60 per m², large interlocking tiles about 10 to 11 and natural slates 12 to 21, depending on size and headlap. Enter your roof below for tiles or slates, battens, and ridge and hip tiles, worked out from manufacturer data.

Roof size

Measure the roof by

Add each roof slope, or a group of matching slopes. A hipped roof needs a section for the main slopes and one for the hip ends.

Roof section 1

Slope length

Eaves to ridge, measured on the roof.

Width

Along the eaves. For a hip end or other sloping shape, use the average width.

Slopes like this

2 for a simple gable roof.

Tiles or slates

Tile or slate

Marley Modern, a large-format interlocking tile, 420 × 330 mm: 345 mm maximum gauge (75 mm headlap), 292 mm cover. Use 320 mm gauge (100 mm headlap) on lower pitches.

Gauge (batten spacing)

Cover width

Check the manufacturer’s minimum pitch and headlap for your roof. Low pitches and exposed sites need more headlap, so a smaller gauge.

Ridge and hips

Ridge length

Total of all ridges.

Ridge and hip tile length

457 mm for standard Marley and Russell concrete ridges. Check yours.

Length of each hip

Along the hip, eaves to ridge. 0 if none.

Number of hips

4 for a fully hipped roof.

Verges (optional)

Length of each verge

Along the slope at the gable edge.

Number of verges

4 for a simple gable roof.

Waste and battens

Waste

5% for a simple roof. More for hips, valleys and dormers: we suggest 10%.

Batten length

4.8 m is a common merchant length. Match your supplier.

834 tiles · 243.5 m battens Breakdown

Tiles to order

834 tiles

80 m² of roof at 9.9 per m², plus 5% waste.

Roof area: 80 m²
Gauge and cover: 345 mm × 292 mm
Tiles per m²: 9.9
Tiles before waste: 794.1
Tiles with 5% waste: 834
Battens: 243.5 m (51 × 4.8 m)
Ridge tiles: 18 (8 m)

Estimate for ordering only. Figures come from the manufacturer data named on this page. Check your own tile’s data sheet, minimum pitch, headlap and fixing specification before you order.

How the roof tile calculator works

It does the same sums as a roofer’s take-off, using figures from the tile maker’s data sheet.

Roof area. Each slope’s length from eaves to ridge, times its width along the eaves. For a hip end or other sloping shape, use the average width: half the base for a triangle. If you measure on plan, the calculator divides the plan area by the cosine of the pitch. A 35° roof has about 22% more area than its footprint.
Tiles per m². (1,000 ÷ gauge) × (1,000 ÷ cover width), in mm. That’s courses per metre times tiles per metre of course. For slates, the gauge is (slate length − headlap) ÷ 2 and the cover width is the slate width.
Tiles to order. Area × tiles per m², plus waste, rounded up to a whole tile.
Battens. 1,000 ÷ gauge metres per m², one run per course, plus the same waste. Divided by the batten length and rounded up.
Ridge and hips. Length ÷ ridge tile length, rounded up. Each hip is counted on its own, so a cut tile on every hip is allowed for.
Verges, if you add them. Courses at each verge = verge length ÷ gauge. Plain tiles and slates take a tile-and-a-half or slate-and-a-half in alternate courses. Dry verge units fit one per course.

It gives quantities only, not fixings or wind uplift. It doesn’t count the eaves and top tiles a plain tile roof needs for its double courses, or valley tiles.

Worked example

A gable roof with two slopes, each 5 m from eaves to ridge and 8 m along the eaves. Marley Modern tiles at their 345 mm maximum gauge, with a 292 mm cover. There’s 8 m of ridge, and 5% waste.

Roof area: 5 × 8 × 2 = 80 m²
Tiles per m²: (1,000 ÷ 345) × (1,000 ÷ 292) = 9.927. Marley’s data sheet says 9.9.
Tiles: 80 × 9.927 = 794, plus 5% and rounded up = 834 tiles
Battens: 80 × (1,000 ÷ 345) = 231.9 m, plus 5% = 243.5 m. That’s 243.5 ÷ 4.8 = 50.7, so 51 lengths of 4.8 m
Ridge: 8,000 ÷ 457 = 17.5, so 18 ridge tiles

The same roof in plain tiles at 100 mm gauge works out at 60.6 tiles per m². That’s 5,091 tiles and 840 m of battens with 5% waste, about six times as many tiles.

Tiles and slates per m²

Tiles and slates per m², as published
Tile or slate	Size (mm)	Gauge (mm)	Per m²	Source
Plain tile, Redland Rosemary (clay)	265 × 165	100 (max)	60	Redland
Plain tile, Marley (concrete)	267 × 168	100 (max)	60	Marley
Marley Modern	420 × 330	345 (max)	9.9, or 10.7 at 100 mm headlap	Marley
Marley Ludlow Major	420 × 330	345 (max)	9.8, or 10.6 at 100 mm headlap	Marley
Russell Grampian	418 × 330	343 (max)	9.8, or 10.6 at 100 mm headlap	Russell
Marley Double Roman	420 × 330	345 (max)	9.7, or 10.4 at 100 mm headlap	Marley
Natural slate	500 × 250	210 at 80 mm headlap	19.0, or 20.0 at 100 mm headlap	SSQ
Natural slate	600 × 300	260 at 80 mm headlap	12.8, or 13.3 at 100 mm headlap	SSQ

Net figures, before waste. Interlocking tiles show the maximum gauge at 75 mm headlap. Slate figures follow SSQ’s coverage table.

Natural slate headlap by pitch

Slate headlap depends on the pitch and how much driving rain the roof gets. SSQ publishes these minimums to BS 5534. Other slate makers publish their own tables, and they differ, so use your slate’s.

SSQ minimum headlap (mm) for natural slates, nail or hook fixing
Slate (mm) and exposure	20°	22.5°	25°	27.5°	30°	35°	40°	45°	80°
500 × 250, moderate	–	150	120	100	80	70	60	55	50
500 × 250, severe	–	–	–	130	100	90	80	70	65
600 × 300, moderate	130	120	95	85	80	70	60	55	50
600 × 300, severe	150	140	130	120	100	90	80	70	65

Moderate exposure is under 56.5 litres/m² per spell of driving rain; severe is 56.5 or more. A dash means SSQ gives no figure at that pitch.

FAQ

Questions about roof tiles

How do I calculate how many roof tiles I need?

Work out the roof area in m², multiply it by the tiles per m² for your tile at your gauge, then add waste and round up.

Measure each slope on the roof itself, from eaves to ridge and along the eaves. The floor area of the house is smaller than the roof. If you can only measure from the ground or from drawings, use the plan size and the pitch, and the calculator converts it.

How many roof tiles per m²?

It depends on the tile and the gauge. Plain tiles need about 60 per m² at 100 mm gauge (Marley and Redland). Large interlocking concrete tiles such as Marley Modern, Double Roman and Russell Grampian need 9.7 to 9.9 per m² at their maximum gauge, and about 10.4 to 10.7 at 100 mm headlap. Use the figure on your tile’s data sheet. The table above lists the ones we checked.

How many roof tiles do you need for a 3 bedroom house?

There’s no standard number, because roof sizes and tiles vary, so measure your own roof. As a guide, the 80 m² gable roof in the worked example needs 834 large interlocking tiles with 5% waste, or 5,091 plain tiles. A hipped roof on the same house means far more cutting, so allow more waste.

How many slates do I need?

Find the gauge first: (slate length − headlap) ÷ 2. Slates per m² is then 1,000,000 ÷ (gauge × slate width), all in mm. A 500 × 250 mm slate at 80 mm headlap has a 210 mm gauge, so 19.0 slates per m². A 600 × 300 mm slate at the same headlap needs 12.8. Both match SSQ’s coverage table. Cupa Pizarras allows a 5 mm gap between slates in its table, which gives slightly fewer.

How much waste should I allow?

We start at 5%, the least Cupa Pizarras recommends for slate. Allow more where there’s a lot of cutting: hips, valleys, dormers and roof windows. We suggest 10% for those roofs. The calculator adds the same waste to battens. Ridge and hip tiles are rounded up but get nothing extra.

What are gauge and headlap?

Gauge is the distance between battens, which is how much of each tile shows. Headlap is how far a tile overlaps the one below. For interlocking tiles, gauge is tile length minus headlap: Marley Modern is 420 − 75 = 345 mm. Plain tiles and slates are double lapped, so the headlap is over the tile two courses down and the gauge is (length − headlap) ÷ 2. Low pitches and exposed sites need more headlap, which means a smaller gauge and more tiles.