How the calculation works
The calculator converts dimensions to meters and calculates each surface as a rectangle, circle, or triangle. It adds the areas, multiplies by explicit material depth, applies the editable settling or extra allowance, and divides by the declared bag volume before rounding up to whole bags.
US example
A 10 ft by 10 ft bed covered 3 in deep needs exactly 25 cu ft. With no settling allowance and 2 cu ft bags, the purchase quantity is 13 bags.
Metric example
A 3 m by 3 m bed covered 7.5 cm deep needs 0.675 m³, or 675 liters. With 50 liter bags and no extra allowance, the purchase quantity is 14 bags.
Choose the right surface shape
Use length times width for rectangular beds. Use diameter for a circle. Use base and perpendicular height for a triangle. Advanced mode can add another rectangular bed, while the formula engine supports mixed named shapes for detailed projects.
Depth drives the result
Volume equals area times depth, so a small depth change can substantially change the order. The calculator begins at 3 in and displays 7.5 cm after switching to metric. This value is editable and is not a universal recommendation for mulch, soil, compost, gravel, or another material.
Bags and bulk material
Enter the volume on the bag in cubic feet or liters. The result rounds up to whole bags. For a bulk quote, compare the adjusted cubic-foot or cubic-meter result with the supplier’s sales unit and minimum order. Confirm whether delivery quantities are loose, compacted, or rounded by container size.
Limitations
- Suitable depth depends on the material, existing layer, plants, drainage, weed goals, compaction, and local conditions.
- Loose and bulk materials can settle, vary in moisture, or be sold using rounded loader or container volumes.
- The calculator estimates volume only and does not determine soil chemistry, amendments, plant suitability, or drainage design.
Frequently asked questions
Why is the default mulch depth 3 inches?
It is an editable planning starting point within a commonly discussed range for mulch. The right depth depends on material and site conditions.
Can I combine circles and rectangles?
Yes. Advanced calculations support named rectangle, circle, and triangle areas that are added before depth is applied.
Should I add a settling allowance?
Use it when the material is expected to settle or when the measured surface is uneven. Supplier guidance and past experience can inform the percentage.
Sources
Sources support unit conventions, product variability, and project limitations. They do not endorse this calculator.