Made for a little less guesswork
About us
Free Mulch Calculator is a free online planning tool for homeowners, gardeners and anyone preparing garden beds. Our goal is simple: help you turn measurements into a clear estimate of how much mulch to buy, with the maths and assumptions easy to understand.
What you can plan
Estimate mulch for a single flower bed, tree ring or a whole garden. Combine different bed shapes, switch between imperial and metric units, choose your bag size and account for mulch already on the ground. You can also compare bagged and bulk costs using your own supplier quotes, share a plan or print it for your shopping trip.
The calculator is independent of mulch retailers and suppliers. We do not sell mulch or provide live prices, stock availability, delivery services or landscaping work. There is no account or payment required to use the tool.
Our calculation method
We calculate each bed’s area using standard geometry, multiply by the number of identical beds, then add the areas. Measurements are converted to metres internally using exact unit definitions. A foot is 0.3048 metres; a cubic yard is 0.764554857984 cubic metres, or 27 cubic feet.
Fresh mulch depth is the desired total depth minus the existing layer, with a minimum of zero. Volume is area multiplied by fresh depth. Your optional allowance increases that volume by the percentage entered. Whole bags are rounded up once, after all beds have been combined.
For example, a 20 × 5 foot bed has an area of 100 square feet. A fresh 3-inch layer requires 100 × 3 ÷ 12 = 25 cubic feet, or approximately 0.93 cubic yards. With 2-cubic-foot bags, that means buying 13 whole bags before any extra allowance.
Shapes and measurements
- Rectangle: length × width. Square: side².
- Circle: π × (diameter ÷ 2)². Tree ring: outer circle area minus inner circle area.
- Circle border: an inner diameter plus an outward border width. Rectangular border: an inner length and width plus an outward border width.
- Triangle: base × perpendicular height ÷ 2, or Heron’s formula for three valid sides.
- Trapezoid: (parallel side A + parallel side B) × perpendicular height ÷ 2.
- Known area: your stated area, converted to square metres.
Costs and practical limits
Bag cost uses whole bags multiplied by price per bag. Bulk quantity is rounded up to your supplier’s order increment, then multiplied by the price per unit, with your delivery fee added when an order is needed. Tax, spreading labour and bag delivery charges are separate. Currency selection changes the display; it does not convert prices using exchange rates. Check supplier minimum orders separately.
All beds in a plan share the same depth settings. Use separate plans when beds need different depths. The tool estimates volume, not material weight, and actual coverage depends on your measurements, the product and ground conditions.
How we approach gardening information
Our general depth guidance draws on the Royal Horticultural Society and University of Maryland Extension. Different plants, mulch textures and drainage conditions may need different treatment. Garden depth suggestions do not establish safe playground surfacing.
We welcome reports of calculation errors, unclear explanations and accessibility problems. Contact us with the inputs and result so we can review the issue.