Mulch Calculator

Depth, Not Area, Is Where Mulch Orders Go Wrong

Two gardeners with identical bed sizes can end up with wildly different mulch orders depending on whether they spread it 1 inch deep as a light refresh or 4 inches deep to smother weeds — and because volume scales directly with depth, that choice matters as much as the square footage itself.

The Formula

Area is entered in square feet and depth in inches, so the calculator divides depth by 12 to convert it to feet before multiplying by area, giving a volume in cubic feet. That figure is then converted to cubic yards (dividing by 27, the unit most bulk mulch is sold and delivered in) and to bagged units, assuming the standard 2 cu ft bag size sold at most garden centers.

Where This Calculation Matters

• New garden beds — a fresh bed typically wants 3 inches of mulch, the depth generally recommended for effective weed suppression without smothering plant roots.
• Annual top-dressing — refreshing existing mulch usually needs only 1 to 2 inches, since older material underneath still provides most of the coverage.
• Bulk vs. bagged buying — bulk delivery by the cubic yard is typically cheaper per unit for large beds, while bagged mulch avoids minimum delivery quantities for small areas.

Mulch Needed by Depth (100 sq ft Bed)

A depth of 2 to 3 inches is the range most commonly recommended for garden beds — enough to suppress weeds and retain soil moisture without restricting airflow to the soil.

How to Use This Calculator

1. Enter the bed or garden Area in square feet.
2. Optionally enter the Depth in inches — defaults to 3 in, the standard recommended mulch depth.
3. Select Calculate to see the volume in cubic yards and the equivalent number of standard 2 cu ft bags.

Related Calculations

Laying sod in the same yard? The Sod Calculator covers lawn areas, and the Gravel Calculator handles pathways bordering the mulched beds.