Home & construction
Gravel and mulch calculator
Bulk materials are quoted by volume, delivered by weight and priced by either. Enter the area and depth once and get all three, for the material you are actually buying.
2–3 inches for decorative gravel and mulch, 4–6 inches for a driveable surface over a base.
Volume is easy, weight is the useful part
Area times depth gives volume, and that part is straightforward. The complication is that suppliers deliver by weight, quote by the ton or the cubic yard depending on the material, and every material has a different density.
The spread is enormous. A cubic metre of bark mulch weighs about 400 kg. The same volume of road base weighs over 2200. Ordering “two tons” of each gets you five times as much bark by volume as stone — which is why quoting the wrong unit to a supplier produces expensive surprises.
Typical densities
| Material | Tonnes per m³ | US tons per cu yd |
|---|---|---|
| Bark mulch | 0.40 | 0.34 |
| Wood chip | 0.75 | 0.63 |
| Topsoil | 1.30 | 1.10 |
| Compost | 1.44 | 1.21 |
| Dry sand | 1.52 | 1.28 |
| Gravel | 1.68 | 1.42 |
| Road base / MOT type 1 | 2.24 | 1.89 |
These are loose, reasonably dry figures. Rain adds weight without adding volume, so a rained-on load can weigh 10–20% more than the same material dry. If you are paying by weight, that matters.
Depth by purpose
Depth is where most of the cost sits, since doubling it doubles the order.
- Decorative gravel — 50 mm (2 in) over a membrane. Deeper looks good but walks badly.
- Mulch on beds — 50–75 mm (2–3 in). Enough to suppress weeds, not so much that it holds water against stems.
- Path or driveway surface — 50 mm of gravel over a compacted 100–150 mm base.
- Topsoil for new lawn — 100–150 mm (4–6 in) of usable depth.
Keep mulch clear of tree trunks and plant stems. Piling it against bark traps moisture and invites rot, a mistake common enough to have its own name among arborists.
Settling, and ordering a little over
Loose material compacts. Gravel under foot and vehicle traffic settles by roughly 10%, and freshly delivered mulch settles as it breaks down. Ordering at exactly the calculated depth leaves you slightly shallow within a few months.
Bulk delivery is dramatically cheaper per unit than bagged material once you pass about half a cubic yard, though it needs somewhere for the tipper to drop and somebody to barrow it. Bagged is worth the premium only for small jobs or where access is genuinely impossible.
Common questions
How many cubic yards of gravel do I need?
Multiply length by width in feet, multiply by depth in feet, then divide by 27. A 20 by 10 foot area at 3 inches deep is 20 × 10 × 0.25 = 50 cubic feet, or 1.85 cubic yards. At typical gravel density that is roughly 2.6 US tons.
How much does a cubic yard of gravel weigh?
Roughly 1.4 US tons, or 1.3 tonnes, when dry. Wet gravel is heavier by 10 to 20 percent. Denser materials like crushed road base run closer to 1.9 tons per cubic yard, while mulch is under half a ton.
How deep should mulch be?
Two to three inches over beds. Less than that will not suppress weeds; much more can starve roots of air and hold moisture against stems. Keep it pulled back from trunks and stems rather than mounded against them.
Should I order by volume or by weight?
Whichever your supplier quotes, but always convert and check both. The same nominal order in tons and cubic yards can differ by a factor of five between bark and stone. Confirming the density they are working from avoids a delivery that is half or double what you expected.