Fire Pit Calculator — Fire Bricks, Mortar & Cap Stones

Lay the bricks as stretchers (230mm length running around the ring) and divide the ring circumference by the brick length plus mortar joint. For a 1m inside-diameter pit the bricks sit on a centreline circle of about 1.11m (inside diameter + one 114mm wall), so circumference ≈ 3.5m ÷ (230mm + 10mm joint = 0.24m) ≈ 15 bricks per course. With 4 courses high that's about 60 fire bricks. Add 10% for cuts and breakages.

Use fire bricks (refractory bricks) for the inner ring as they withstand temperatures up to 1,300°C. Standard bricks will crack and spall from heat cycling. Fire bricks are typically 230mm × 114mm × 65mm. For the outer decorative ring, standard engineering bricks or natural stone are fine as they don't contact flames directly.

Yes, fire pits need drainage to prevent rainwater pooling in the base. Lay 100-150mm of clean shingle (10mm pea shingle or 20mm washed gravel — the larger 20mm grade drains best) in the base before use. Don't use concrete for the base — it can crack from heat and trap water. Some builders also install a 50mm drain pipe through the base for complete drainage.

Use fire cement or refractory mortar for the inner ring of fire bricks — standard mortar will crack at high temperatures. For the outer ring (if using standard bricks), normal mortar is fine. Fire cement is available in tubs from builders' merchants. Apply in thin joints (5-10mm) between fire bricks.

A permanent fire pit structure doesn't usually need planning permission if it's in your garden and is a reasonable size. However, check with your local council about smoke control zones — in a Smoke Control Area you can only burn authorised smokeless or Ready-to-Burn fuels. Keep the fire pit at least 3m (3–6m where space allows) from boundaries, fences, sheds, trees and any flammable structures, with at least 6m vertical clearance below any pergola or overhanging branches. Be considerate of neighbours.