Use π multiplied by radius squared to find area, then multiply by soil depth. The calculator accepts diameter and converts it to radius internally.
Round area planning tool
Circular Garden Soil Calculator
Calculate topsoil for circular beds, round lawns, planters and tree rings using outer diameter, optional inner diameter and fill depth.
No signupUS & metricInstant results
Calculate a circle or planting ring
Use ring mode when the centre will not be filled.
Estimated result
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Enter the project details and calculate.
Circular geometry
Diameter is not radius
The calculator asks for diameter because it is easier to measure across a garden feature. It divides by two internally before applying π × radius².
Full circles
Use a full circle for round beds, lawns or planters that will be filled across the centre.
Rings
Use ring mode when a central circle remains unfilled, such as a tree surround or planting ring.
π × (outer radius² − inner radius²) × depthTree care caution
More soil is not always better around an established tree
Adding a deep layer against a trunk can bury the root flare and change oxygen or moisture conditions. The calculator provides quantity, not permission to alter tree grade.
For valuable or mature trees, confirm the design with a qualified arborist and keep new soil or mulch away from direct trunk contact.
Measuring tip
Measure more than one diameter when the circle is imperfect
Many real garden beds are oval or irregular. Measure across two directions and use an average diameter, or divide the area into simpler sections with the multi-area calculator.
Small irregularity
An average diameter may be adequate for a roughly circular bed.
Large irregularity
Split the shape into rectangles and circles rather than forcing one inaccurate diameter.
Frequently asked questions
Circular soil calculator questions
Ring mode subtracts the unfilled central circle from the outer circle, which is useful for tree surrounds and annular beds.
No. The inner diameter must be smaller because it represents the empty centre within the outer circle.
The volume can be estimated, but altering soil depth around a tree can affect its health. Confirm the design before adding soil against the root zone or trunk.