How do I mark out a circular bed on the ground?

Push a stake into the centre and tie a string to it at exactly half the diameter (the radius) — for a 3 m bed that is 1.5 m. Pull the string taut and walk a full loop, marking the edge with dry sand, line marker or spray paint. For a semi-circle or quarter, peg the straight edges first then swing the string between them.

What edging works best for circular beds?

Flexible steel edging or corrugated plastic edging bends around tight curves without kinking and gives a crisp line. Victorian rope-top tiles suit period gardens, while log roll is the budget choice for gentle curves. Brick or stone setts look best but each unit must be cut or angled to follow the arc, so allow extra for offcuts.

How deep should a circular flower bed be?

Dig to at least 300 mm for most perennials and annuals so roots have room and drainage is good. If the existing soil is poor, build a raised circular bed 200-400 mm above ground level and fill with a topsoil/compost mix. The RHS recommends improving heavy or sandy soils with bulky organic matter before planting.

How much topsoil or compost do I need to fill the bed?

Multiply the bed area by the fill depth in metres to get cubic metres. A 3 m full circle is 7.07 m²; filling it 300 mm (0.3 m) deep needs 7.07 × 0.3 = 2.12 m³, which is roughly four 0.6 m³ bulk bags of topsoil. Compost is sold by the litre (1 m³ = 1,000 L), so the same volume is about 2,120 L — around 35 of the 60 L bags.

How do I convert the diameter to the radius?

The radius is always half the diameter, so divide the diameter by two: a 3 m diameter bed has a 1.5 m radius. Measure the diameter across the widest point of the marked circle, through the centre stake. Area uses the radius (πr²) while the full-circle perimeter uses the diameter (πd), so getting this conversion right keeps both figures correct.

GardenCalcs

Circular Bed Calculator — Round Flower Bed Area & Edging

Calculate area and edging for circular or semi-circular flower beds.

Bed TypeFull circle, semi-circle (one straight flat diameter edge) or quarter circle (two straight radius edges)

Diameter

Width across the widest point through the centre — the radius is half this

Edging price per metre (optional)

Cost per linear metre of your chosen edging — leave at 0 to skip the cost estimate

Include 10% wastage for edging

Adds the waste percentage below to cover offcuts where curved edging is trimmed to fit

How We Calculate This

Full circle: Area = π × radius² and perimeter = π × diameter. Semi-circle: area is half the full circle, perimeter = π × radius + diameter (the curved arc plus the straight flat edge). Quarter circle: area is one quarter, perimeter = π × radius ÷ 2 + 2 × radius (the arc plus the two straight radius edges).

Edging length is the full perimeter of the bed, so it includes the straight flat edges on semi- and quarter-circle beds, not just the curve.

The wastage allowance (10% by default, adjustable under Advanced options) covers offcuts where rigid edging has to be cut to follow the curve.

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates based on standard gardening guidelines. Results may vary with soil conditions, climate, and plant varieties.