Mulch Calculator
Mulch suppresses weeds and holds soil moisture — but only at the right depth. This calculator takes your bed dimensions and target depth and returns cubic yards to order, how many 2- and 3-cubic-foot bags that equals, the coverage you will get at a 3-inch depth, and an estimated weight by mulch type. Use it before the garden-center run so you buy once.
3 in is the sweet spot for weed suppression; 2 in for top-ups.
Type affects the weight estimate only — volume is the same.
Mulch needed
1.85yd³
- 2-cu-ft bagsOne cubic yard fills 13.5 two-cubic-foot bags.
- 25
- 3-cu-ft bagsOne cubic yard fills 9 three-cubic-foot bags.
- 17
- Coverage at 3 in depthSquare feet this order covers if spread 3 in deep.
- 200ft²
- Estimated weightshredded hardwood ≈ 0.5 tons per yard.
- 0.93ton
How it was calculated
- Volume: 20 ft × 10 ft × 0.250 ft = 50.00 ft³ = 1.85 yd³.
- 2-cu-ft bags: 1.85 × 13.5 = 25.0 → 25 bags (rounded up).
- Coverage: 1.85 yd³ × 108 ft² per yard at 3 in = 200.0 ft².
How it works
Volume = length × width × depth (in feet), divided by 27 for cubic yards — the unit bulk mulch is sold in.
Bag equivalents come from the yard itself: 1 yd³ = 27 ft³, so it fills 13.5 two-cubic-foot bags or 9 three-cubic-foot bags, always rounded up.
Coverage at 3 inches: one yard spread 0.25 ft deep covers 27 ÷ 0.25 = 108 ft². Multiply by your yards for the total.
Weight = yards × the mulch type's bulk density (hardwood 0.5, pine bark 0.4, cedar 0.6 tons per yard) — useful for delivery planning, not for the volume math.
Worked examples
20 × 10 ft bed at 3 inches, shredded hardwood
Volume = 200 × 0.25 = 50 ft³ = 1.85 yd³. That is 25 two-cubic-foot bags (1.85 × 13.5 = 25.0) or 17 three-cubic-foot bags. Coverage at 3 in: 1.85 × 108 = 200 ft² — exactly the bed area. Weight ≈ 0.93 tons.
10 × 10 ft bed at 2 inches, cedar
Volume = 100 × 0.1667 = 16.67 ft³ = 0.62 yd³. Two-cubic-foot bags: 0.62 × 13.5 = 8.3 → 9 bags. Coverage at 3 in would be 66.7 ft², but at your 2-inch depth the order covers the full 100 ft². Weight ≈ 0.37 tons.
How to measure
- Measure each bed separately — L-shaped and curved beds estimated as one rectangle always overshoot.
- For curved beds, measure the average width at three points and use the middle value.
- Keep mulch 2–3 inches away from tree trunks and house siding to prevent rot and pests.
- Measure depth from the soil surface, and remember existing mulch counts — top-ups need only 1–2 in.
- For a refresh of last year's beds, halve the depth in the calculator rather than re-measuring everything.
Assumptions & limitations
Planning estimate
- Mulch densities (hardwood ≈ 0.5, pine bark ≈ 0.4, cedar ≈ 0.6 tons per cubic yard) are a rule of thumb — wet mulch can weigh substantially more than dry.
- Volume assumes level beds at a uniform depth; mounded or bermed beds need extra.
- Bag counts assume bags are full to their labeled volume; settling in the bag can make real-world counts slightly higher.
- The 3-inch depth is the standard weed-suppression recommendation; vegetable gardens often use less.
Frequently asked questions
Three inches is the standard for weed suppression and moisture retention in ornamental beds. Use 2 inches for annual top-ups over existing mulch, and 4 inches maximum — deeper layers can suffocate roots and invite rodents.
One cubic yard equals 13.5 two-cubic-foot bags or 9 three-cubic-foot bags. A 20 × 10 ft bed at 3 inches needs 1.85 yards, which is 25 two-cubic-foot bags. Bulk delivery is usually cheaper once you pass about 3 yards.
Bulk is almost always cheaper per cubic yard, often by 30–50%, but suppliers usually require a 1–3 yard minimum and charge a delivery fee. Bagged mulch wins for small beds, precise colors, and when you have no place to dump a pile.
No — volume is volume. The type only changes the weight and the look: shredded hardwood knits together and stays put on slopes, pine bark is lighter and acidic (good for azaleas), and cedar lasts longest and repels insects.
Most bark mulches decompose within a year. Top up with 1–2 inches each spring rather than replacing everything — measure the existing depth first and enter only the additional depth you need.