This mulch calculator converts your bed dimensions and target depth into cubic yards and bag counts. Enter the bed’s length and width (or its total square footage), choose a depth, and you will know whether to grab a few bags or order a bulk delivery.
The math hinges on one number worth memorizing: a cubic yard of mulch covers 324 square feet at 1 inch deep. At the standard 3-inch depth for weed suppression, that same yard covers 108 square feet — so beds eat mulch faster than most people expect.
The Mulch Formula
Volume in cubic feet = area (sq ft) × depth (inches) ÷ 12, then divide by 27 for cubic yards:
- 200 sq ft at 3 inches = 200 × 0.25 = 50 cubic feet = 1.85 cubic yards
- In bags: 50 ÷ 2 = 25 two-cubic-foot bags, or 17 three-cubic-foot bags
Quick reference for one cubic yard: 324 sq ft at 1", 162 sq ft at 2", 108 sq ft at 3", 81 sq ft at 4".
How Deep Should Mulch Be?
Depth is a horticultural decision, not just a cost one:
- 1 inch: refreshing beds that already have mulch — rake the old layer first
- 2 inches: fine mulches like shredded hardwood in low-weed beds
- 3 inches: the standard recommendation for moisture retention and weed suppression
- 4 inches: coarse mulches (pine bark nuggets) or beds with heavy weed pressure
Avoid going deeper than 4 inches: thick mulch suffocates roots, holds excess moisture against stems, and invites rot. Keep mulch 2–3 inches away from tree trunks and plant crowns — the “mulch volcano” piled against a trunk is the most common landscaping mistake and slowly kills trees.
Bags vs. Bulk Delivery
A cubic yard equals 13.5 two-cubic-foot bags or 9 three-cubic-foot bags. Bagged mulch typically works out to $45–$80 per cubic yard equivalent, while bulk mulch runs $25–$50 per yard plus delivery.
Rules of thumb:
- Under 1 yard (about 13 bags): bags win — no delivery fee, easy to move, no pile on the driveway
- 1–3 yards: compare bulk-plus-delivery against bag pricing; sales change the answer
- Over 3 yards: bulk almost always wins, and one delivery saves dozens of bag trips
A standard full-size pickup bed can haul 2–3 cubic yards of mulch (it is light, unlike gravel or soil).
Frequently Asked Questions
How much does a yard of mulch cover?
One cubic yard covers 324 square feet at 1 inch deep. At the standard 3-inch depth it covers 108 square feet, and at 2 inches it covers 162 square feet. Divide 324 by your depth in inches for coverage at any depth.
How many bags of mulch are in a cubic yard?
A cubic yard is 27 cubic feet, so it equals 13.5 of the common 2-cubic-foot bags or 9 of the 3-cubic-foot bags. If you need more than about a dozen bags, price out bulk delivery — it is usually significantly cheaper per yard.
How deep should mulch be to stop weeds?
Three inches is the sweet spot for most beds: deep enough to block light from weed seeds and hold soil moisture, shallow enough not to suffocate plant roots. Use 4 inches only with coarse mulches like bark nuggets, and never pile mulch against trunks or stems.
How much mulch do I need for 100 square feet?
At 3 inches deep, 100 square feet needs 25 cubic feet — that is 0.93 cubic yards, 13 two-cubic-foot bags, or 9 three-cubic-foot bags. At 2 inches deep it drops to about 17 cubic feet, or 9 two-cubic-foot bags.
When is the best time to mulch?
Mid-to-late spring, after the soil has warmed, is ideal — mulching too early keeps soil cold and delays growth. A lighter fall top-up insulates roots for winter. Most beds need a 1-inch refresh once a year as the mulch decomposes into the soil.