How the fire pit and paver calculator works
Choose your project, enter the measurements and the calculator tells you how many blocks, pavers, gravel and sand to buy. There are three tabs:
- Fire pit ring: the number of blocks for a round fire pit, the gravel for its base, and the fill for the inside.
- Paver patio: the number of pavers with waste, the gravel base, the bedding sand and the edge restraint.
- Gravel or sand area: the volume and weight of any loose material, for a path, a bed, or a pad.
How many blocks for a fire pit?
The blocks sit in a ring, so the number in each course is the distance round the centre of the ring divided by the length of a block. For a 36 in pit built with blocks 12 in long and 8 in deep, the ring is about 138 in round, which takes 12 blocks per course. Three courses take 36 blocks, plus a cap layer if you want one.
Stacking blocks on top of each other in a staggered pattern makes a stronger wall, and a landscape adhesive keeps them from shifting.
What goes under and inside a fire pit?
- Base: dig out about 4 to 6 in, make it level, and fill it with compacted gravel. The base should be about 6 in wider than the blocks on each side.
- Inside: line the inside with fire brick or a steel ring, and fill the bottom with lava rock or crushed fire-safe gravel.
- Avoid river rock and ordinary concrete blocks inside the pit. Wet stone can crack or burst in the heat.
Fire pit safety
- Keep the fire pit at least 10 to 25 ft from buildings, fences, trees and overhanging branches. Check local rules, as many places set their own distance.
- Do not build it on a wooden deck, or under a roof.
- Keep a bucket of water, sand or a hose nearby.
- Check local burn bans and rules before using it.
How many pavers for a patio?
Divide the area of the patio by the area of one paver plus its joint, and add extra for the cuts and breakage. The extra depends on the pattern:
| Pattern | Extra |
|---|---|
| Grid or stack bond | 5% |
| Running bond or basketweave | 10% |
| Herringbone, diagonal or circular | 15% |
How deep should the base be?
| Use | Gravel base |
|---|---|
| Patio or path in a mild climate | 4 in |
| Cold climate or clay soil | 6 in |
| Driveway or heavy use | 8 in or more |
On top of the gravel, spread a layer of coarse sand about 1 in deep, and set the pavers in it. The calculator adds 20% to the gravel for compaction, and 10% to the sand.
Worked examples
A 36 in fire pit ring, 3 courses
You need 36 blocks, 12 per course. The gravel base is about 64 in across, and needs about 0.33 yd³ at 4 in deep. The inside fill is about 0.13 yd³ of lava rock at 6 in deep.
A 12 ft × 12 ft patio with 12 × 12 in pavers
With a 1/8 in joint and a grid pattern, you need 149 pavers. The 4 in gravel base needs about 2.1 yd³, or 3 tons. The sand layer needs about 0.5 yd³, and the edge restraint is 48 ft.
A 10 ft × 10 ft gravel pad, 3 in deep
You need about 0.93 yd³, which weighs about 1.3 tons, or about 50 bags of 0.5 cubic feet.
Common mistakes
- Skipping the base. Pavers on bare soil sink, shift and tip. The compacted gravel is what holds them.
- Using the wrong sand. Use coarse bedding sand, not fine play sand, which washes away.
- Forgetting the edge restraint. Without it, the pavers spread out at the edge.
- Not leaving a slope. A patio needs a fall of about 1/4 in per foot away from the house, so water runs off.
- Ordering exactly the amount you need. Gravel settles and spreads, and pavers break.
Tips
- Compact the gravel in layers of 2 to 3 in with a plate compactor, which you can hire for a day.
- Buy all the pavers at once, so the colour matches, and mix them from different pallets as you lay them.
- Cut pavers with a wet saw, or a masonry blade on an angle grinder, and wear eye and ear protection.
- Call before you dig. Most places have a free service that marks buried cables and pipes.
