How the BBQ calculator works
A classic garden BBQ is a U-shaped brick plinth: a back wall plus two side walls with the front left open, with steel brackets or brick corbels holding the charcoal tray and grill. The calculator works out the wall area and multiplies by 60 bricks per m² (single skin) or 120 per m² (double skin):
Firebricks are assumed to be 230 × 114mm laid flat on the charcoal bed and on edge 250mm up the back and sides. One 2kg tub of fire cement beds about 18 firebricks.
Building tips
- Choose frost-resistant (F2) facing bricks for the outside, and engineering bricks for the bottom courses if the ground is wet.
- Buy your grill and charcoal tray first and set out the internal width to fit them with a 2–3mm expansion gap.
- Build in brick ledges (turn a brick sideways) or fix brackets at the right course for the tray and grill.
- Use a 4:1 mortar with plasticiser and a 3:1 mix for the top courses and copings.
- Cap the walls with paving slabs or copings to stop water soaking into the brickwork.
Worked example: a 1.8m U-shaped BBQ
A BBQ 1.8m wide and 0.7m deep has 1.8 + 0.7 + 0.7 = 3.2m of wall. At 0.9m high (12 courses) that's 2.88m², and in single-skin brick at 60 bricks per m² plus 10% it needs 191 bricks. Mortar for them is about 170kg dry: 2 bags of cement and 6 small bags of building sand. Lining a 700 × 500mm firebox takes about 33 firebricks and 2 tubs of fire cement. A 100mm concrete base 2.0m × 0.9m is about 0.2m³, which is 3 bags of cement and roughly 340kg of ballast mixed by hand.
A double-skin build looks more solid and gives wider tops for resting plates, but roughly doubles the bricks. Add a centre divider for log or charcoal storage and it grows by another side wall.
Choosing the spot
- Away from fences, sheds and overhanging trees. Leave a good clear space round the firebox. Timber fences can scorch and catch fire.
- Think about smoke. Check which way the wind usually blows in your garden, and avoid sending smoke over the house or next door's windows.
- Close to the kitchen, on firm level ground. A patio edge is ideal. Building on loose soil or a lawn needs a proper slab.
- Plan the worktop. A slab or two on top of a side wall makes a useful prep surface. Include it in your width.
First use
Let the mortar cure for at least a week, longer in cold weather, before lighting a fire. Start with a small fire to dry out the firebricks and fire cement gently. A full-heat first fire can crack damp brickwork. Keep a lid or cover over the grill area in winter to stop rain soaking the firebox.
Common mistakes
- Building before buying the grill. Kits come in set sizes. Measure the tray and grill first, then set out the bricks to fit.
- Ordinary bricks in the fire. Facing bricks and cement mortar crack at charcoal temperatures. Use firebricks and fire cement for the fire area.
- No base. A brick BBQ is heavy, and without a slab it can sink unevenly and crack.
For more on bricks and mortar per square metre and firebricks, read our brick and mortar guide. Mix the base with help from the concrete calculator, or build a matching wall with the brick calculator.