Mulch Calculator

A mulch calculator uses one formula: cubic yards = area in square feet × depth in inches ÷ 324. A 24 × 4 ft bed is 96 sq ft, so 3 inches of mulch takes 96 × 3 ÷ 324 ≈ 0.89 cu yd, which is 24 cu ft: twelve 2 cu ft bags or eight 3 cu ft bags.

How to use the mulch calculator

1. Add one row per bed and pick its shape: rectangle, circle, tree ring, half circle, triangle, trapezoid, border strip, an irregular four-sided bed, or a known area. Use Count for several identical beds, such as a ring around each of three trees.
2. Type sizes in feet and inches (or meters and centimeters). Use Subtract for a path or patio inside a bed.
3. Pick a depth guide or type your own depth. If old mulch is still there, enter its depth and the calculator adds only the difference.
4. Set the extra for settling, then check the bag sizes. Type bag and bulk prices to see which is cheaper.
5. Open “Show steps” to see each bed’s area and the conversions.

The mulch formula, step by step

• Area of each bed: rectangle = length × width; circle = π × diameter² ÷ 4; tree ring = π × (outer diameter² − inner diameter²) ÷ 4; triangle = base × height ÷ 2.
• Volume in cubic feet = area × depth in inches ÷ 12.
• Cubic yards = cubic feet ÷ 27. Dividing by 12 and then by 27 is the same as dividing by 324, which is where the one-line formula comes from.
• Bags = cubic feet ÷ bag size, rounded up. A cubic yard holds 13.5 bags of 2 cu ft or 9 bags of 3 cu ft.
• Top-up: depth to add = target depth − depth already there.

In metric: cubic meters = area in m² × depth in cm ÷ 100, and 1 m³ = 1,000 liters.

How deep should mulch be?

Extension services give these depths for organic mulch such as wood chips and shredded bark:

Both sources warn against piling mulch against trunks. Iowa State says to keep it at least 6 inches away from tree trunks; Clemson says to leave at least a hand’s width of space around trunks and stems. The tree ring shape handles this: set the inner diameter to the bare circle you will leave around the trunk.

Worked examples

Example 1: three kinds of beds

A front bed 24 × 4 ft is 96 sq ft. A corner bed shaped like a triangle with an 8 ft base and 6 ft height is 8 × 6 ÷ 2 = 24 sq ft. Two tree rings 6 ft across with a 1 ft bare circle are π × (6² − 1²) ÷ 4 ≈ 27.49 sq ft each, or 54.98 sq ft together. The total is 96 + 24 + 54.98 = 174.98 sq ft.

At 3 in: 174.98 × 3 ÷ 324 ≈ 1.62 cu yd (43.74 cu ft). With 5% extra for settling, 43.74 × 1.05 ≈ 45.93 cu ft, or 1.7 cu yd. In bags: 45.93 ÷ 2 ≈ 22.97, so 23 bags of 2 cu ft; or 45.93 ÷ 3 ≈ 15.31, so 16 bags of 3 cu ft.

Example 2: topping up old mulch

The 96 sq ft front bed still has about 1 in of old mulch, and you want 3 in. Add only 3 − 1 = 2 in: 96 × 2 ÷ 324 ≈ 0.59 cu yd, which is 16 cu ft. With 5% extra that is 16.8 cu ft, or 6 bags of 3 cu ft (16.8 ÷ 3 = 5.6, rounded up).

Example 3: bags or bulk?

For the 1.7 cu yd in Example 1, say a 3 cu ft bag costs $5 and bulk mulch costs $40 per cubic yard plus $60 delivery (use your local prices). Bags: 16 × 5 = $80. Bulk: 1.7 × 40 + 60 = $128. Here bags win. For a big job of 6 cu yd, bags would take 54 bags ($270), while bulk costs 6 × 40 + 60 = $300; with a lower bulk price or pickup instead of delivery, bulk soon wins. The calculator does this comparison for your numbers.

Quick reference: how far a bag or a yard goes

Coverage = bag volume in cubic feet × 12 ÷ depth in inches. For a cubic yard it is 324 ÷ depth.

Common mistakes

• Treating inches as feet. 3 in is 0.25 ft. Multiplying the area by 3 instead of 0.25 makes the order twelve times too big.
• Dividing by 9 instead of 27. There are 9 sq ft in a square yard but 27 cu ft in a cubic yard.
• Counting a tree ring as a full circle. Leave the bare area around the trunk out; it also protects the tree.
• Ignoring old mulch. Adding a full 3 in on top of 2 in of old mulch gives 5 in, deeper than the extension ranges above.
• Using the radius as the diameter. The circle formulas here use the full distance across.

Real-life uses

Plan spring mulching for all the beds around a house in one list, compare bagged mulch with a bulk delivery, work out a ring for every tree on a street front with Count, or price mulch for a school or community garden. The same volume math works for compost, wood chips and bark. For stone instead of wood mulch, the gravel calculator adds weight in tons.

Results are estimates. Mulch settles, beds are rarely perfect shapes and bag fills vary, so a little extra is sensible.

Sources

• Iowa State University Extension and Outreach: How deep should the mulch layer be around trees and shrubs? (checked November 2026)
• Clemson Cooperative Extension, Carolina Yards: Mulch matters (checked November 2026)
• NIST Handbook 44, Appendix C: general tables of units of measurement (27 cu ft = 1 cu yd; 1 cu ft = 28.316846592 L; checked November 2026)

Mulch volume practice quiz: 10 questions

Test yourself with 10 multiple-choice questions. Choose an answer and press Submit to see if you are right and why. Your score appears at the end.

Frequently asked questions

How much mulch do I need for a 10 × 10 bed?

At 3 in deep: 100 × 3 ÷ 324 ≈ 0.93 cu yd, which is 25 cu ft. That is 13 bags of 2 cu ft or 9 bags of 3 cu ft.

How many bags of mulch are in a yard?

A cubic yard is 27 cu ft, so it equals 13.5 bags of 2 cu ft (buy 14) or exactly 9 bags of 3 cu ft.

How many square feet does a yard of mulch cover?

Divide 324 by the depth in inches: 162 sq ft at 2 in, 108 sq ft at 3 in and 81 sq ft at 4 in.

How deep should mulch be?

Clemson Extension recommends 2 to 3 inches in plant beds and around trees and shrubs. Iowa State Extension suggests 3 to 4 inches of wood chips or shredded bark around trees and shrubs on well-drained sites and 2 to 3 inches on heavy soils.

Should I remove old mulch first?

Not always. If the old layer is thin, you can top it up. Enter its depth under “Mulch already there” and the calculator only adds what is missing to reach your target.

Related calculators

• Gravel calculator for stone, with tons
• Square footage calculator
• Volume calculator
• Circle calculator for round beds