Gravel & Mulch Calculator
Figure out how much bulk material your project needs — in cubic yards, tons, bags, and dollars — for beds, paths, and driveways.
Weights are typical loose densities — actual weight depends on moisture and compaction. Order bulk material by cubic yard (1 yd³ = 27 ft³); delivery minimums usually start around 5–10 yd³.
How the volume math works
Every bulk order comes down to one box: area times depth. Measure the footprint in feet and the depth in inches, then divide by 12 to get feet. That step is the one people skip.
Volume (ft³) = Length (ft) × Width (ft) × Depth (in) ÷ 12
A 20-ft × 10-ft bed is 200 ft². At 3″ deep: 3 ÷ 12 = 0.25 ft, and 200 × 0.25 = 50 ft³. Irregular beds are smaller boxes added together — split them into rectangles and triangles, add them up, then round up.
From cubic feet to cubic yards and tons
Yards quote by the cubic yard. One cubic yard is 27 cubic feet — a box 3 ft × 3 ft × 3 ft.
Cubic yards = Cubic feet ÷ 27
Weight depends on the material, not the volume. Typical loose densities, in tons per cubic yard:
- Mulch / wood chips — 0.35 t/yd³
- Compost — 0.5 t/yd³
- Topsoil — 0.95 t/yd³
- Sand — 1.2 t/yd³
- Crushed stone — 1.35 t/yd³
- Gravel / pea gravel — 1.4 t/yd³
That same 50 ft³ is 1.85 yd³ — about 0.65 tons as mulch, about 2.59 tons as gravel (1.85 × 1.4). Use these figures to plan and compare quotes; moisture makes the real weight differ.
Recommended depth: mulch
Mulch is the one material where more is not better. Too thin and weeds come through; too thick and water sheds off the top, roots stay shallow, and the layer underneath goes matted.
- Wood chips / arborist mulch: 3–4″ is best; never over 4″
- Bark: never over 3″; fine-textured bark, 2–3″
- Flower and vegetable beds: 2–3″
- Weed suppression: at least 3″ to smother germinating weed seed
Keep it off the trunk and root flare of trees: 2–3″ at the trunk, pulled back off the bark. Reapply on schedule — bark every 2–4 years, wood chips every 1–2 years — and mulch lightly, if at all, on wet, poorly drained ground.
A fresh bed and a refresh are different jobs
A new bed gets the full depth in one pass — that layer is the one doing the weed work. A refresh is a top-up: mulch decays, so the depth you measure is what is actually there. Rake it back, measure, and order only the difference. If a bed holds 2″ and you want the 3–4″ band, you are buying 1–2″, not another full 3″.
Recommended depth: gravel
Gravel depth is set by what travels over it.
- Paths and walkways: 2–3″ of loose surface over compacted subgrade
- Driveways: 4–6″ compacted, in lifts of about 4″ so each layer compacts before the next goes down
You will also see 3–4″ quoted for paths. Both are legitimate — the difference is traffic. Two to three inches is a proper pedestrian surface; three to four is what installers quote for a path that takes a wheelbarrow and still has to hold its crown.
On a driveway, compacted means finished compacted — spread, roll, water, drive on it. A geotextile under the stone is standard over soft ground; installers who sell it report losing 2–3″ a year without one — a vendor claim, not a tested figure.
Drainage is different: a French drain or dry well is sized around the pipe and its surrounding stone, not by a surface depth.
A worked example you can check by hand
A 20-ft × 10-ft bed, wood-chip mulch, spread at 3″.
- Area: 20 × 10 = 200 ft²
- Depth in feet: 3 ÷ 12 = 0.25 ft
- Volume: 200 × 0.25 = 50 ft³
- Cubic yards: 50 ÷ 27 = 1.85 yd³
- With the 10% allowance: 50 × 1.10 = 55 ft³, and 55 ÷ 27 = 2.04 yd³. Order 2 cubic yards.
- Weight: 2.04 × 0.35 = about 0.71 tons.
- Bags: 55 ÷ 2 = 27.5, so 28 two-cubic-foot bags.
Check it the other way: one yard covers 108 ft² at 3″, so 200 ÷ 108 = 1.85 yd³ — same as step four.
Settling, compaction, and ordering over
Two things eat material after it lands. Mulch settles and decays, so the layer you spread is thinner by fall. Gravel compacts: stone spread loose is not stone until it has been rolled and watered.
That is the justification for the allowance: a yard short means a second delivery minimum and a half-finished bed exposed while you wait. On gravel, lift thickness matters as much as total depth — 6″ dumped in one pass does not compact through. Use angular crushed stone for anything carrying a vehicle; rounded pea gravel rolls out from under a tire.
Bags versus bulk delivery
Bagged mulch and compost come in 2-cubic-foot bags, which is the bag count the calculator reports for those materials: 28 trips from the truck to the bed in our example.
Bulk wins on price and labour, but only if you can take the load. Yards commonly set delivery minimums around 5–10 cubic yards, and some add a short-load fee below that. A yard of mulch rides in a pickup; a yard of gravel is about 1.4 tons and needs a trailer or a delivery.
Common mistakes
- Multiplying the area by inches. Convert depth to feet first, or the whole order is off by a factor of 12.
- Forgetting the settling allowance. What arrives is loose; what stays is compacted. Order about 10% over.
- Burying the root flare. Wide rings, 2–3″ at the trunk, pulled back off the bark.
- Re-spreading full depth on a refresh. You end up past the 4-inch ceiling; top up to the band instead.
- Gravel straight onto bare soil. Loose stone punched into soft ground disappears. Paths want 2–3″ over compacted subgrade.
- Heavy mulch on wet ground. Poorly drained beds take light mulch or none.
Gravel and mulch FAQ
How much area does a cubic yard of mulch cover?
At 3″ deep, one cubic yard covers 108 ft² — the rule of thumb is about 100 ft² at 3″. One yard is 27 ft³, so at 3″ (0.25 ft) you get 27 ÷ 0.25 = 108 ft².
How deep should mulch be in a garden bed?
Two to four inches is the safe band. Wood chips should not exceed 4″ and perform best at 3–4″; bark should not exceed 3″, and fine-textured bark wants 2–3″. You need at least 3″ to smother germinating weed seed. Keep mulch off the trunk and root flare — 2–3″ at the trunk, pulled back off the bark.
How deep should gravel be for a driveway?
Four to six inches of compacted stone, spread in lifts of about 4″ so each layer locks up. Gravel paths take 2–3″ of loose surface over compacted subgrade. The depth quoted is finished compacted depth — the material you buy is deeper than that.
How many cubic feet are in a cubic yard?
Twenty-seven. A cubic yard is 3 ft × 3 ft × 3 ft = 27 ft³, so divide cubic feet by 27. A 50-ft³ order is 1.85 yd³, and with a 10% allowance for settling you would order 2 yards.
Related
Spreading stone for a shed pad or a slab instead of a bed? Start with the concrete calculator and the concrete slab guide. Setting deck posts? The deck footing calculator covers footing size and concrete per hole.