Mulch Calculator

How much mulch do I need?

Mulch is sold by volume, so the job is to turn the area of your beds and the depth you want into cubic yards (bulk) or cubic feet (bags). Multiply area by depth, keeping the units consistent. In US units, depth in inches is divided by 12 to get feet:

Cubic feet = Length (ft) × Width (ft) × Depth (in) ÷ 12
Cubic yards = Cubic feet ÷ 27
Bags = Cubic feet ÷ bag size (cu ft), rounded up

Worked example: a 24 ft × 6 ft border at 3 inches deep is 144 sq ft × 0.25 ft = 36 cu ft, which is 1.33 cubic yards. In bags, that's 18 two-cubic-foot bags or 12 three-cubic-foot bags. A shortcut worth remembering: one cubic yard covers 324 sq ft at 1 inch deep, so divide 324 by your depth in inches to get the coverage of one yard. At 3 inches, a yard covers 108 sq ft.

In metric, depth in centimetres is divided by 100: a 6 m × 1.5 m bed at 7.5 cm needs 0.680 m³, or 675 litres, which is 14 bags of 50 L. If you don't already know the area, the square footage calculator handles L-shapes and other awkward layouts.

How deep should mulch be?

University of Illinois Extension recommends a mulch layer of 2 to 4 inches (about 5–10 cm) on well-drained sites. Within that range, it suggests 2–3 inches for composted materials and 3–4 inches for coarse mulches such as bark nuggets and wood chips. Nebraska Extension's Backyard Farmer program gives the same 2–4 inch range for most organic mulches and notes that 1–2 inches may be enough for heavier materials like gravel. That's why this calculator starts at 3 inches.

More is not better. Illinois Extension warns that thick layers can mat down and reduce water and oxygen reaching the soil, keep the root zone too wet, and give rodents cover. Mulch should also stay clear of trunks and stems: its guidance is to keep it at least 4 inches away from the trunk and never pile it up the bark in a "volcano", which can soften the bark and lead to decay, pests and girdling roots.

If you are topping up an existing bed, measure what's there first (push a trowel down and check the depth) and enter only the extra depth you need, not the full 3 inches.

Sources: University of Illinois Extension, "Proper Mulching Techniques" (2024); Nebraska Extension Backyard Farmer, "Mulch".

Mulch coverage by depth

How much mulch 100 sq ft of bed (for example 10 × 10 ft, or 25 × 4 ft) needs at common depths, and how far a single cubic yard goes. Bag counts are rounded up to whole bags.

The same figures in metric, per 10 m² of bed:

Bags vs bulk: how many bags make a yard

A cubic yard is 27 cubic feet, so it takes 13.5 bags of 2 cu ft or 9 bags of 3 cu ft to equal one yard of bulk mulch. In metric, a cubic metre is 1,000 litres: 20 bags of 50 L or about 13⅓ bags of 75 L. Note that a 2 cu ft bag holds about 57 L and a 3 cu ft bag about 85 L, so switching the calculator to metric changes the bag size slightly, not just the label.

Bags are easier for small jobs, top-ups and places a delivery truck can't reach, and they keep tidily until you need them. Bulk mulch from a landscape yard is usually cheaper per cubic yard once the job runs to a few yards, though suppliers may add a delivery charge or set a minimum order. The fair comparison is cost per cubic yard: enter both a bulk price and a bag price above, and the calculator prices the same volume both ways. Prices vary widely by region, material and season, so use local quotes rather than national averages.

Bulk is sold by the scoop, and suppliers typically load in half- or whole-yard steps. If the result is 1.33 yd³, you'll be ordering 1 yard. Bagged mulch is rounded up to whole bags here for the same reason.

Round, irregular and multiple beds

For a circular bed or a tree ring, choose Circle and enter the diameter. The calculator uses area = π × (diameter ÷ 2)². A 6 ft ring around a tree is about 28.3 sq ft, which at 3 inches deep is 7.1 cu ft, or 4 bags of 2 cu ft.

Most yards have several beds. Add each one as its own row and the calculator totals them. For example, a 30 × 4 ft foundation bed, a 12 × 8 ft island and an 8 ft circle around a tree come to 266 sq ft. At 3 inches that is 2.47 cubic yards, or 34 two-cubic-foot bags.

Irregular, curvy beds can be approximated by splitting them into a few rectangles and circles. Another way is to measure the longest length and the average of three or four widths. Small errors in width matter more than you'd expect: a bed that is 6 ft wide on average rather than 5 needs 20% more mulch.

Topsoil, compost and other materials

The volume math doesn't care what the material is, so you can use this calculator for topsoil, garden soil, compost, sand for a play area, or rubber mulch. Enter the depth your project calls for and use the bag size printed on the product. Bagged soils and composts are labelled in cubic feet or litres, just like mulch. Loose soil and compost settle after they're watered in, so many gardeners buy a little extra when filling raised beds.

For gravel, crushed stone and decorative rock, use the gravel calculator instead. Stone is normally sold by the ton, and that calculator converts volume into weight using typical densities. For a concrete edging strip or a slab next to the beds, the concrete calculator gives cubic yards and bag counts.

Sources

The formulas on this page come from the published research below. Last updated October 10, 2026. This calculator gives estimates for general information. It isn't medical advice, so check anything important with a qualified professional.

1. Vogel S, Lee J. Proper Mulching Techniques (Tree Care Basics). University of Illinois Extension; modified March 2024.Used for: Recommended 2–4 inch mulch depth and keeping mulch at least 4 inches from trunks
2. Backyard Farmer: Mulch. Nebraska Extension, University of Nebraska–Lincoln IANR.Used for: 2–4 inch depth for most organic mulches; 1–2 inches for heavier materials