What the Mulch Calculator does
This mulch calculator works out how much mulch, bark, compost or decorative gravel you need: describe each bed - rectangle, circle, ring round a tree, triangle or an irregular shape - choose the depth, and it gives the volume in cubic yards, cubic feet, cubic metres and litres, the number of bags of each common size, and the cost if you add prices.
The sum is area times depth, but the units are where it goes wrong: bed sizes in feet, depth in inches, bags in cubic feet and bulk deliveries in cubic yards. Every conversion here uses the exact definitions, bags are always rounded up to whole bags, and nothing you enter leaves your browser.
How to use it
- Choose feet and inches or metres and centimetres. US results lead with cubic yards; metric results with cubic metres and litres.
- Add each bed. Pick its shape and enter its measurements; for an irregular bed, measure its length and several widths across it and the calculator uses their average. Use "How many like this" for identical beds.
- Set the depth. For most beds 2 to 3 inches (5 to 8 cm) is the depth extension services suggest; add an allowance for settling and spillage if you want some to spare.
- Choose the bag size you will buy and, optionally, the price per bag and the bulk price per cubic yard or cubic metre.
- Read the total at the top, the bags of every size in the bar chart, and the breakdown per bed. Copy, download or print the list for the garden centre.
Reading the results
The headline volume already includes the extra allowance. Fresh mulch settles and compacts after watering, so a layer spread at 3 inches can end up nearer 2.5; an allowance of around 10% is a common way to cover that and the odd spill.
Bag counts are rounded up, because you cannot buy part of a bag. That is why a slightly smaller or larger bag size can change the cost more than you would expect - compare the bars.
Bulk suppliers usually sell by the cubic yard or cubic metre, often in half-yard steps. Bulk is generally better value for large areas but has delivery costs; bags are easier for small beds and tight access.
Gravel and stone are calculated the same way by volume, but they are often sold by weight. Ask your supplier for the weight per cubic yard or per cubic metre of the product, because it varies with stone size and type.
Worked example: two front beds and a tree ring, 3 inches deep
Two front beds are 12 ft x 4 ft each: 2 x 48 = 96 sq ft. A ring round a maple is 6 ft across with a 1 ft trunk, so its area is pi / 4 x (6^2 - 1^2) = 0.7854 x 35 = 27.49 sq ft. Together that is 123.49 sq ft.
At 3 inches deep (0.25 ft) the volume is 123.49 x 0.25 = 30.87 cu ft. Adding 10% for settling gives 33.96 cu ft, and dividing by 27 gives 1.26 cubic yards (0.96 cubic metres).
In 2 cu ft bags that is 33.96 / 2 = 16.98, so 17 bags; at 4.50 a bag that is 76.50. In 3 cu ft bags it is 11.3, so 12 bags.
Bulk, 1.26 cubic yards at 40 a yard is about 50.31 before delivery, and a supplier selling in half yards would deliver 1.5 cubic yards.
Formulas and scoring rules
- Volume
volume = sum of bed areas x depth x (1 + extra % / 100)- Bed areas
rectangle L x W; circle pi x d^2 / 4; tree ring pi / 4 x (D^2 - d^2); triangle b x h / 2; irregular L x average(widths)- Cubic yards
cu yd = cu ft / 271 ft = 0.3048 m exactly, so 1 cu ft = 0.028316846592 m^3 and 1 cu yd = 0.764554857984 m^3.- Bags
bags = ceiling(volume / bag volume)Rounded up, because a part bag still has to be bought. Volumes are displayed to 2 decimal places.- Coverage
area covered = volume / depth; 1 cu yd covers 324 sq ft at 1 in, 108 sq ft at 3 in
Limitations: what the result does not prove
- Measurements are only as good as the tape: curved beds measured by the average-width method can be off by several percent, so measure more widths where the shape changes.
- Bag volumes are taken as printed. Some products are packed loose and some compressed (compressed bales expand when opened), so check the label for the loose volume.
- It does not decide what material or depth is right for your plants or soil. Keep mulch a few inches away from stems and trunks, and follow local guidance for slopes, drainage and fire risk.
- Prices are whatever you enter. Delivery charges, minimum orders and taxes are not included.
Privacy: where your data goes
Everything you paste, type or drop is processed in this browser tab. It is not uploaded, logged, stored or sent to analytics. Session recording and tag-manager scripts are switched off on this page.
Standards and sources
- NIST SP 811 - Guide for the Use of the International System of Units - checked 19 Sep 2026
- Clemson Cooperative Extension - Mulch matters
- University of Illinois Extension - Mulch madness
- UF/IFAS Gardening Solutions - Mulch
Frequently asked questions
How much mulch do I need?
Multiply the bed's area by the depth in the same units. A 10 ft x 4 ft bed at 3 inches is 40 sq ft x 0.25 ft = 10 cu ft, which is 10 / 27 = 0.37 cubic yards or five 2 cu ft bags. Enter all your beds here to get the total, bags and cost at once.
How many bags of mulch are in a cubic yard?
A cubic yard is 27 cubic feet, so it takes 13.5 bags of 2 cu ft (14 in practice), 9 bags of 3 cu ft or 18 bags of 1.5 cu ft. In metric terms a cubic yard is about 765 litres, roughly 16 bags of 50 litres.
How deep should mulch be?
University extension services such as Clemson, the University of Florida and Illinois generally suggest 2 to 3 inches (5 to 8 cm) once settled, and warn against going deeper than about 4 inches because it can restrict air and water to roots. Keep it pulled back from trunks and stems.
How many square feet does a yard of mulch cover?
At 1 inch deep, one cubic yard covers 324 sq ft. At 2 inches it covers 162 sq ft, at 3 inches 108 sq ft and at 4 inches 81 sq ft. In metric, a cubic metre covers 20 square metres at 5 cm or about 13 at 7.5 cm.
How do I measure an irregular or curved bed?
Measure its longest length, then measure the width across it at several evenly spaced points and average them. Length times average width is a good estimate of the area. Choose "Irregular (average width)" and enter the widths separated by commas; more widths give a better estimate.
How much mulch do I need around a tree?
Treat it as a ring: the area is pi / 4 x (outer diameter squared minus trunk diameter squared). A ring 6 ft across round a 1 ft trunk is 27.5 sq ft, which at 3 inches needs about 6.9 cu ft - four 2 cu ft bags. Keep the mulch a few inches clear of the trunk itself.
Can I use this for gravel, topsoil or compost?
Yes for the volume: the geometry is the same for any loose material. Gravel and soil are often sold by weight, though, so ask the supplier how many tonnes make a cubic yard or cubic metre of their product before ordering.
Last reviewed by the A2Z.Tools team against the sources listed above.
