How much mulch do I need?
The volume of mulch is the area you want to cover multiplied by the depth of the layer. Enter the area (or the length and width of each bed), the depth, and optionally a waste allowance, and the calculator returns the volume in cubic feet, cubic yards, cubic metres and litres at the same time, so you can compare it with a bag label or a supplier's quote in whatever unit they use. For 100 square feet at 3 inches deep the volume is 25 cubic feet, which is 0.9259 cubic yards or 0.7079 cubic metres.
The formula, step by step
Convert the depth to the same unit as the area, then multiply. In US units: volume in cubic feet = area in square feet × depth in inches ÷ 12. For 100 ft² at 3 inches that is 100 × 3 ÷ 12 = 25 cubic feet. One cubic yard is 27 cubic feet, so 25 ÷ 27 = 0.9259 cubic yards. In metric units: volume in cubic metres = area in square metres × depth in centimetres ÷ 100. For 10 m² at 7.5 cm the volume is 0.75 cubic metres, or 750 litres. The calculator uses the exact international definitions (1 foot is exactly 0.3048 metres, 1 inch is 0.0254 metres, 1 litre is exactly 0.001 cubic metres), so every unit agrees with every other to the last digit shown.
What depth should I use?
Depth depends on the purpose. Many extension services suggest roughly 2 to 4 inches (5 to 10 cm) of organic mulch around trees, shrubs and flower beds, kept away from the trunks and stems, with thinner layers for fine-textured mulches that pack down and slightly thicker ones for coarse chips. Weed suppression needs more depth than looks alone. Land-grant university extension services publish local guidance, for example the Proper Mulching Techniques info sheet (University of Illinois Extension), which recommends a 2 to 4 inch layer kept off the trunk. Deeper is not better: a very thick layer can hold too much water and keep air from roots. Going from 3 to 4 inches over 400 square feet raises the requirement to 133.33 cubic feet.
Counting whole bags
Bags are sold whole, so the number of bags is the required volume divided by the bag size, rounded up. With a 2 cubic foot bag, 25 cubic feet needs 12.5 bags, so you buy 13 and have 1 ft³ left over. If the volume happens to be an exact multiple of the bag size, no extra bag is added: 104 square feet at 3 inches is 26 cubic feet, which is exactly 13 bags with nothing left over. The bag icons in the results show the last bag filled only as far as you would use it, which makes it easy to decide whether to buy the last bag or trim the area. Bag sizes vary by brand, so check the label: US bags are commonly 1, 1.5, 2 or 3 cubic feet, and metric bags are often 50, 60 or 70 litres. Enter your bag's size in cubic feet or litres.
The waste allowance
Mulch settles, spills and gets spread unevenly, and beds are rarely perfect rectangles, so many people add a small margin. The waste field adds a percentage to the volume, once. Adding 10% to the 100 ft², 3-inch example raises the requirement from 25 to 27.5 cubic feet and the bag count from 13 to 14. The default is 0% so that the figure you see is the plain geometric answer; choose a margin that matches how carefully you spread.
Measuring irregular beds
For a curved or irregular bed, break the shape into rectangles (and triangles), measure each one, and use the beds mode to add up to ten of them. Each bed has its own length and width units, so you can mix feet and inches. If you need to measure an area from a plan, the square footage calculator handles several shapes. The same volume method works for other loose materials: use the gravel calculator for stone and the concrete calculator for slabs and footings.
Bagged or bulk: comparing the cost
Bags are convenient and cost more per unit of mulch; bulk delivery is usually cheaper per cubic yard but may add a delivery charge and needs somewhere to put the pile. To compare them, enter the bag price and the bulk price per cubic yard or cubic metre, and optionally a delivery charge. With bags at 4.50 each and bulk at 35 per cubic yard, the 25 cubic feet job costs 58.50 in bags and 32.41 in bulk before delivery. A delivery charge of 60 would bring the bulk total to 92.41, and the page then recomputes which option is cheaper. The comparison assumes bulk is charged on the exact volume with no minimum load, and that delivery applies to bulk only; a supplier with a minimum order or a step price will differ, so treat the result as an estimate and confirm with the supplier. A blank price means "not entered" and produces no cost at all, whereas 0 means free. If you leave out the bag size and bag price the page still reports the volume and the bulk cost.
Typing numbers correctly
Use a dot for decimals and no thousands separators. A comma is rejected on purpose because it can mean different things in different countries, and a blank required field is an error, never a zero. Area and depth must be greater than zero, the waste allowance must be between 0% and 100%, and prices cannot be negative. Each field accepts up to 12 digits and 6 decimal places. Related checks: round your final figures with the rounding calculator.
Mulch calculator questions
How many bags of mulch do I need for 100 square feet?
At 3 inches deep you need 25 cubic feet, which is 13 bags of 2 cubic feet. At other depths or bag sizes the number changes, so enter yours.
How many cubic yards of mulch is that?
Divide cubic feet by 27. For 25 cubic feet that is 0.9259 cubic yards.
How deep should mulch be?
Roughly 2 to 4 inches (5 to 10 cm) is the usual range for garden beds, depending on the material and your local extension advice. Keep it clear of trunks and stems.
Should I add extra for waste?
A small margin such as 5% to 10% is common, especially for irregular beds. Enter it in the waste field; it is applied once to the volume.
Is bulk cheaper than bagged mulch?
Usually per cubic yard, but delivery charges and minimum loads can change that for small jobs. Enter both prices and the delivery charge to compare for your quantity.
Why is my bag count a whole number?
Bags are sold whole, so the count is rounded up. The leftover amount is shown so you can decide whether the last bag is worth buying.