What is the standard roof pitch in the UK?

The most common roof pitch for UK houses is between 30° and 45°. New-build houses typically have a pitch of around 35-40°. This range works well with most tile types and provides good weather resistance. Older Victorian and Edwardian properties often have steeper pitches of 40-50°. Minimum pitch for most tiles is around 22.5° but always check the tile manufacturer's specifications. Once you know the pitch, use our Roof Area Calculator to convert plan area to actual sloping roof area.

How do I measure roof pitch?

From inside the loft: hold a spirit level horizontally from a rafter and measure 1 metre along it. Then measure vertically from that point down to the rafter — this is the rise per metre. Use tan(angle) = rise/run to calculate degrees. From outside: measure the vertical height from the top of the wall plate to the ridge, and the horizontal distance from the wall to directly below the ridge (half the span).

What is the minimum pitch for roof tiles?

Minimum pitches vary by tile type. Concrete interlocking tiles: typically 15-22.5° minimum. Plain clay tiles: 35° minimum. Natural slate: 20-25° minimum (depends on slate size and headlap). Large format tiles: 15-17.5° minimum. For pitches below 10°, you will need a flat roof membrane — see our Flat Roof Membrane Calculator. Use our Roof Tile Calculator to work out tile quantities once you know the pitch is suitable.

What does a 4:12 roof pitch mean?

A 4:12 pitch means the roof rises 4 units vertically for every 12 units of horizontal run. This is approximately 18.4 degrees. The X:12 ratio system is common in both the UK and US for describing roof pitch. A 6:12 pitch (26.6°) and 8:12 pitch (33.7°) are considered moderate to standard UK pitches.

Does roof pitch affect planning permission?

Roof pitch can affect planning permission, particularly for extensions and conversions. Many Local Planning Authorities require new roof slopes to match the existing roof pitch. Permitted Development rights for rear extensions often specify that the roof pitch must match the original house. Altering the pitch of an existing roof usually requires planning permission.

Roof Pitch Calculator — Degrees, Ratio and Rafter Length

How We Calculate This

Our roof pitch calculator determines the angle of your roof slope from either rise and run measurements, or from the total span and ridge height. It displays the result in degrees, as a ratio and as a percentage gradient.

The formula

Pitch (degrees) = arctan(Rise ÷ Run)
Pitch (%) = (Rise ÷ Run) × 100
Pitch ratio = (Rise ÷ Run) × 12 : 12

If using span and ridge height: Run = Span ÷ 2, then apply the same formula.

Common UK pitch ranges

Under 10°: Flat roof — requires membrane (EPDM, GRP, built-up felt)
10-15°: Very low pitch — specialist tiles or metal sheeting only
15-22.5°: Low pitch — interlocking tiles, some large format slates
22.5-30°: Moderate — most interlocking tiles and slates
30-45°: Standard UK pitch — all tile types suitable
45-60°: Steep — traditional look, excellent weather protection

The calculator also shows the rafter length (the sloping distance from eaves to ridge), which is useful for ordering materials like battens and felt.

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates. Verify with your supplier.

Roof Pitch Calculator — Degrees, Ratio & Percentage