The plan
Decorative gravel is bought by weight, and the calculator converts the volume into tonnes at 1.50 tonnes per cubic metre for loose decorative stone. It also gives the bulk-bag and 25 kg bag counts, because those are the two ways it is actually sold.
The 10% allowance is the calculator's own default, and it is there for ground that is not flat. On a firm, level sub-base you may not need it; the field is yours to change.
Doing it, in order
- Mark the area out with a line, and decide the edge — a timber or steel edge, or a run of setts, is what stops the stone spreading into the border.
- Strip the turf and dig off enough to take the membrane and the stone, so the finished surface ends up just below the surrounding ground.
- Fit the edging first, set to the finished level, so the gravel has something to run up to.
- Lay a woven weed-control membrane over the whole area, lapping the joints by about 100 mm.
- Spread the gravel to a consistent 50 mm and rake it level, working back towards the way you came in.
Don’t forget
- Edging to hold the gravel No engine sizes this, so there is no figure on this page. A gravel edge is a design decision — timber, steel or setts — and its cost depends on which you pick.
- A weed membrane that is woven, not a sheet of polythene Polythene traps water and the gravel turns into a pond. The 14 m² here is the area plus a 10% overlap allowance, from the calculator.
- Bulk bags need somewhere flat and dry The take-off assumes you can take them. Two 850 kg bags is about a tonne and a half of material to move.
- Weeds already in the ground A membrane stops new seed germinating from below. Perennial weeds already rooted will push up through it, so they are worth clearing first.
Material take-off for this plan
Worked out by the site’s own Gravel for this plan’s dimensions, not typed in by hand.
The working
| Working | Value |
|---|---|
| Area to cover | 12.0 m² 4.00 m × 3.00 m |
| Depth | 50 mm 40–75 mm is the usual depth over a weed membrane |
| Volume | 0.66 m³ 0.60 m³ plus 10% allowance |
| Material | Decorative gravel Weighted at 1.50 tonnes per m³ for loose decorative gravel |
| Bulk bags (850 kg) | 2 bags Rounded up to whole bags |
| 25 kg bags | 40 bags Rounded up. Costlier per tonne than bulk — use bulk if you can |
What to order
| Material | Quantity | Notes |
|---|---|---|
| Decorative gravel (loose, by weight) | 0.99 tonnes | Merchants round loosely — about 1.0 t is a practical order. |
| Bulk bags (850 kg) | 2 bags | Needs somewhere flat and dry to sit, and a way to move them. |
| 25 kg bags | 40 bags | ≈ 990 kg in total. Fine for small areas. |
| Weed control fabric / membrane | 14 m² | The area plus 10% for overlaps — stops gravel sinking into the soil. |
Gravel goes down over a woven membrane, not straight onto soil — it stops weeds coming through and stops the stones disappearing into the ground over a few winters. Spread the full depth in one pass, rake it level, and keep it 15–20 mm below damp-proof course level against a wall.
A gravel seating area, planned out FAQs
How much gravel do I need for a 4 m by 3 m area?
0.99 tonnes at a 50 mm depth, using the gravel calculator at its default 10% allowance. That is about 2 bulk bags of 850 kg, or 40 bags of 25 kg.
How deep should gravel be for a seating area?
50 mm is the working figure the calculator starts from, and 40 to 75 mm is the range it treats as usual over a membrane. Deeper is more comfortable underfoot and hides the membrane better.
Is 0.99 tonnes the same as a tonne?
Near enough for ordering. Merchants round loosely, and about 1.0 tonnes is a practical order. The calculator shows the exact figure and the bag counts alongside it.
Do I need a weed membrane under gravel?
Yes — the gravel calculator puts it in the take-off at the area plus 10% for overlaps. Gravel straight onto soil sinks in over a season and weeds come through it.