Mulch and Topsoil Calculator
Cubic yards and bags of mulch, topsoil or compost for a bed, plus guidance on the depth that actually helps.
Mulch & Topsoil Calculator
Cubic yards, bags and what depth to actually use. Depth is the part that matters — too thin does nothing for weeds, too thick suffocates the roots you were trying to protect.
Quick answer: mulch by area and depth
| Area | 3 in.: yd³ / bags | 4 in.: yd³ / bags |
|---|---|---|
| 50 ft² | 0.46 / 7 | 0.62 / 9 |
| 100 ft² | 0.93 / 13 | 1.23 / 17 |
| 150 ft² | 1.39 / 19 | 1.85 / 25 |
| 200 ft² | 1.85 / 25 | 2.47 / 34 |
| 400 ft² | 3.7 / 50 | 4.94 / 67 |
Cubic yards = area × depth (in.) ÷ 12 ÷ 27; bags of 2 ft³, the common mulch bag. Above about a cubic yard, bulk delivery usually beats bags.
| Bed area | — |
|---|---|
| Volume | — |
| Cubic yards | — |
| Bags | — |
| Bulk vs bagged | — |
Depth here is a finished total, not this year's dose. ANSI A300 (Part 2)-2018 §17.4.7 says mulch should be applied and maintained at a depth of 2–4 inches (5–10 cm). Maintained is the word. Last year's mulch is still down there. A 100 ft² bed at 3″ is 0.93 yd³, about 13 bags. The same bed already carrying 2″ needs one inch. That is 0.31 yd³, 5 bags. Three times the order for the same finished depth. §17.4.8 makes the remedy subtraction rather than a thinner top-up: excess mulch should be removed and replaced … to a shallower depth. Push a trowel in, measure what is there, and enter the difference. The flags and the note above read your entry as the finished layer, so a correct one-inch top-up trips the thin-mulch warning. Read it against the bed, not your order.
Mulch is sold by volume because weight is not a legal unit for it. NIST Handbook 130 §2.18.2, the model state weights-and-measures regulation, requires that all mulch shall be sold, offered, or exposed for sale in terms of volume measure. That is cubic yard or cubic foot, cubic meter or liter. Weight is not on the list. EPA's Volume-to-Weight Conversion Factors (April 2016) shows why: a cubic yard of green wood chips weighs 473 lb, the same yard dry 243 lb. By the ton that is 4.2 yd³ against 8.2. Half the mulch for the same money, decided by how wet the pile was. Topsoil is the exception. §2.29(a) lets top soil sold in bulk go by the cubic meter or cubic yard or by weight, so on soil the moisture is legally your problem. Get the yardage on the delivery ticket.
What I check on a job
Walk the bed before you trust it. I don't trust the area until I have walked the bed. Most planting beds are neither the rectangle nor the circle this tool offers, so I break a curved bed into the shapes it is closest to, run each one, and add the yards. Then I take out what will not get mulch: the clear ring I keep around each trunk, paving that cuts into the bed, anything already covered. I check depth in several spots, not one, because the depth at the edge is not the depth in the middle. The figure I distrust most is topsoil. Its depth depends on what is growing and what is underneath, so before I order I dig a test hole to see how much usable soil is already there and what sits under it, then enter only the depth I am adding. The bag count rounds up to whole bags, so at most it carries part of a bag spare; the cubic-yard figure carries none.
One cubic yard is 27 ft³, so a 100 ft² bed at 3″ deep works out at
25 ft³, about 0.93 yd³, or roughly 13 two-cubic-foot bags. That arithmetic is exact.
Depth is a judgement, not a formula. Two to three inches of mulch is a normal refresh; three to
four suppresses weeds and holds moisture better. Deeper is not better. Piling mulch against a
trunk in a mound traps moisture against the bark and invites rot, which is why arborists keep telling
people to pull it back from the stem. Topsoil and compost depths depend entirely on what you are
growing and what is underneath. Bulk delivery usually beats bags somewhere around a cubic yard, but
minimum delivery charges vary, so compare both.
Worked example
A 20 × 5 ft bed, 3 inches of mulch: how many yards, how many bags?
- Area = 100 ft²; volume = 100 × 3/12 = 25 ft³.
- 25 ÷ 27 = 0.93 yd³.
- 2 ft³ bags: ceil(25 ÷ 2) = 13.
Just under a cubic yard, or 13 two-cubic-foot bags. Three inches is the depth that suppresses weeds; two looks fine and does not.
8 values on this page were driven in a browser and compared with independently derived figures on 2026-10-29 (2808 values across 228 calculators site-wide).
Questions
How many bags of mulch in a cubic yard?
13.5 two-cubic-foot bags (27 ÷ 2). A 20 × 5 ft bed at 3 inches needs 25 ft³, or 13 bags.
How deep should mulch be?
About 3 inches to suppress weeds and hold moisture; 2 inches looks fine and does less.
How much mulch for a bed that already has some?
Only the difference. A 100 sq ft bed at 3 in. is 0.93 yd³, about 13 bags; the same bed already carrying 2 in. needs one inch, 0.31 yd³, 5 bags. ANSI A300 (Part 2)-2018 §17.4.7 says applied and maintained at 2 to 4 in.; push a trowel in and measure first.
Why is mulch sold by volume?
Because NIST Handbook 130 §2.18.2, the model state weights-and-measures rule, requires it. EPA's conversion factors show why: a cubic yard of green wood chips weighs 473 lb and the same yard dry 243, so by the ton you could get half the mulch.