Mulch Calculator
How much mulch do you need? Enter your bed size and depth — get cubic yards, bags, bulk-vs-bag cost, and annual re-mulch top-up. Formula: volume = area × depth.
Bed Volume — Cubic Yards & Bags
Depth guidance: 2–4 in around woody plants, 1–2 in around annuals/perennials/vegetables (Univ. of Nebraska Extension); 2–3 in general (Penn State, Mississippi State); 3–4 in around trees, kept 2–3 in away from the trunk (Mississippi State). Deeper than 4 in restricts oxygen to roots (LSU AgCenter).
Bag sizes vary by brand — 2 ft³ is the most common retail bag, but 1, 1.5 and 3 ft³ bags exist. Always check the volume printed on the bag.
Volume Converter
Cost Estimator — Bulk vs Bags
Tip: press "Calculate mulch needed" first — the bed tab fills these fields automatically.
Annual Re-Mulch Top-Up
Organic mulch decomposes roughly 1 inch per year (rule-of-thumb estimate — actual rate depends on material and climate). Enter current and target depth to get the top-up volume.
Coverage per Cubic Yard
Exact math: 1 cubic yard = 27 ft³; square feet covered = 27 ÷ (depth in feet). Suppliers often round 108 down to ~100 ft³ as a rule of thumb.
| Depth | ft² per yd³ | 2-ft³ bags ≈ yd³ |
|---|---|---|
| 1 in | 324 | 13.5 |
| 2 in | 162 | 13.5 |
| 3 in | 108 | 13.5 |
| 4 in | 81 | 13.5 |
| 5 in | 64.8 | 13.5 |
| 6 in | 54 | 13.5 |
Frequently Asked Questions
How do I calculate how much mulch I need?
Multiply bed area by depth: volume (cubic feet) = area (square feet) x depth (feet). Then divide by 27 for cubic yards. Example: a 450 sq ft bed at 3 inches (0.25 ft) needs 450 x 0.25 = 112.5 ft3 = 4.1667 yd3, which is 57 standard 2-ft3 bags (rounded up).
How many bags of mulch are in a cubic yard?
By volume, 13.5 standard 2-ft3 bags make one cubic yard (27 / 2). Since you cannot buy half a bag, plan on 14 bags. For 1.5-ft3 bags it is 18, and for 3-ft3 bags it is 9.
How many square feet does a yard of mulch cover?
Exactly 108 sq ft at 3 inches deep (27 ft3 / 0.25 ft). Coverage per cubic yard: 162 sq ft at 2 in, 108 sq ft at 3 in, 81 sq ft at 4 in. Suppliers often round to a ~100 sq ft rule of thumb at 3 inches.
How deep should mulch be?
University extension guidance: 2-4 inches around woody plants and 1-2 inches around annuals, perennials and vegetables (Univ. of Nebraska Extension); 2-3 inches is sufficient for most beds (Penn State, Mississippi State); 3-4 inches around trees, kept 2-3 inches away from the trunk (Mississippi State). Deeper than 4 inches restricts oxygen to roots (LSU AgCenter).
What is the standard bag size for mulch?
2 cubic feet is the most common retail bag, but 1, 1.5 and 3 ft3 bags also exist and sizes vary by brand - always check the volume printed on the bag, then use the bag-size selector in the calculator above.
Is bulk or bagged mulch cheaper?
Usually bulk, but compare with your local prices. Example: 4.1667 yd3 at $38 per yard = $158.33, versus 57 bags at $4.50 = $256.50 - bulk wins by $98.17 here. Bag sales (for example 5 bags for $10) can flip the math, which is why the Cost tab compares both.
How much mulch do I need for 100 square feet?
At the standard 3-inch depth: 100 x 0.25 = 25 ft3 = 0.9259 yd3, or 13 standard 2-ft3 bags (12.5 rounded up).
How do I calculate mulch for a circular bed?
Area = pi x radius squared. A 6-ft-diameter bed has area 28.2743 sq ft; at 3 inches that is 7.0686 ft3 = 0.2618 yd3. The Bed tab does this automatically - just pick Circle and enter the diameter.
How often should I re-mulch?
Organic mulch decomposes roughly 1 inch per year (a rule-of-thumb estimate; the actual rate depends on material and climate), so most beds need an annual top-up rather than full replacement. Example: topping a 450 sq ft bed from 2 in to 3 in needs 37.5 ft3 = 1.3889 yd3.
What is a mulch volcano and why should I avoid it?
A mulch volcano is mulch piled high against a tree trunk. Mississippi State Extension warns it traps moisture against bark, inviting rot, disease and rodent damage - keep mulch 2-3 inches away from the trunk and never mound it.
Do I need to remove old mulch before adding new?
Usually not for organic mulch - rake out loose debris, measure the remaining settled depth, and top up to your target. Penn State notes the settled depth is what matters for weed control; thin layers under about 2 inches will not smother weeds.
How many cubic meters is a cubic yard of mulch?
0.7646 m3. So 25 ft3 (the 100-sq-ft-at-3-in example) equals 0.7079 m3. Use the Unit Converter tab for yd3 <-> ft3 <-> m3 <-> bags.
- Weight / hauling math — converting cubic yards to tons via material density (mulch, soil, gravel…) is a different job: see our cubic-yards-to-tons calculator (#861, where mulch is one of 20 density presets). This tool answers the opposite question: how much mulch volume your beds need from area × depth.
- Generic area-to-volume conversion — square-feet-to-cubic-yards (#1005) converts any area + depth to yd³. This tool is mulch-specific: bed shapes, extension-based depth recommendations, bulk-vs-bag cost comparison, and annual re-mulch decay.
- Pine straw — sold per bale with its own coverage rate, covered by the upcoming pine-straw spoke tool (#1428). This tool is for bulk (cubic yard) and bagged mulch.
Free tool by NRTechStudio