Mulch Calculator
Buying mulch is a gamble if you eyeball the quantity — you either end up with five extra bags in the driveway or a half-finished bed. This calculator takes length, width and depth of the area you want to cover and returns the volume in cubic feet and cubic yards, the number of 2 cu ft bags, and the cost estimates both ways. Bulk is almost always cheaper per cubic yard, but only if the yardage justifies delivery.
How to calculate mulch quantity
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1
Measure the bed
Length × width in feet. For irregular shapes, break the area into rectangles and add the results.
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2
Choose the depth
2 inches for established perennial beds, 3 inches for weed suppression, 4 inches around trees. More than 4 suffocates roots.
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3
We compute volume
Volume (cu ft) = length × width × (depth / 12). Cubic yards = cu ft / 27. Bags of 2 cu ft each = ceil(cu ft / 2).
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4
Compare cost
Enter bulk price per yard and bag price. The calculator returns the total cost each way so you can pick the cheaper supply route.
How much mulch you actually need
The math is simple but the unit conversions catch people out. Depth is almost always quoted in inches, area in square feet, and bulk sales in cubic yards. Getting from inches to yards involves two divisions (12 to get feet, 27 to get yards).
Quick coverage reference (at 3 inches deep)
| Bed size (ft) | Square feet | Cubic feet | Cubic yards | 2 cu ft bags |
|---|---|---|---|---|
| 4 × 8 | 32 | 8 | 0.30 | 4 |
| 10 × 10 | 100 | 25 | 0.93 | 13 |
| 10 × 20 | 200 | 50 | 1.85 | 25 |
| 15 × 25 | 375 | 94 | 3.47 | 47 |
| 20 × 30 | 600 | 150 | 5.56 | 75 |
| 30 × 50 | 1,500 | 375 | 13.89 | 188 |
Depth guide by purpose
| Depth | Use |
|---|---|
| 1“ | Decorative top-dressing on an already-mulched bed |
| 2“ | Around existing perennials and groundcover |
| 3“ | Standard bed for weed suppression and moisture retention |
| 4“ | Around established trees and shrubs |
| 6“+ | Pathways only — too deep for plant beds |
Never pile mulch against tree trunks or plant stems. “Mulch volcanoes” around trees trap moisture against the bark, invite rodents and can kill the tree within a few years.
Bulk versus bags
- Bulk (cubic yard): Usually $30–$50/yard delivered within 10 miles for hardwood bark. Cheaper per cubic foot but requires a driveway drop zone and a wheelbarrow.
- Bagged (2 cu ft): $4–$8 per bag at retailers. More expensive per cubic foot but trivial to transport and store. Typically makes sense for under ~1.5 cubic yards.
- Bulk break-even: If your bag price is $5 and bulk is $40/yard, bulk wins at roughly 8 bags (16 cu ft / 0.59 yd³). Above 2 cubic yards, bulk is almost always the right call.
Types of mulch and volume differences
- Hardwood bark (most common): 1 yd³ ≈ 500–800 lb.
- Cedar/cypress shredded: similar volume, lighter, ~400–600 lb/yd³.
- Pine straw: sold in bales (~40 sq ft coverage at 3“ depth each), not cubic yards.
- Rubber mulch: 1 yd³ weighs 1,500 lb+ — consider weight limits when ordering.
Settlement
Fresh mulch settles 10–15% in the first month. If you are setting up a new bed for a formal photograph, order 10% extra and spread once, then top up after two weeks.
Frequently Asked Questions
Three inches is the sweet spot for most perennial beds — thick enough to suppress weeds and retain moisture, thin enough not to smother roots. Deeper than 4 inches creates problems; shallower than 2 inches does not do the job.
A cubic yard is 27 cubic feet, so 13.5 bags at 2 cu ft each. Retailers round up — one cubic yard = 14 bags for purchase planning. At $5/bag, that is $70 worth of bags versus $30–$50 in bulk.
Full replacement is unnecessary. Organic mulches decompose from the bottom up, so top-dress 1 inch annually to maintain the 3-inch depth. Full strip-and-replace is only needed if the mulch gets matted, moldy or embedded with weed seeds.
Usually not for planted beds — it prevents mulch from decomposing into the soil and creates a tangled root layer over time. Landscape fabric makes sense only under gravel or decorative stone, where decomposition is not wanted.
No. Your measurements are used once to compute volume and cost and are not stored or shared.
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