Border Area Calculator — Curved & Irregular Borders

Run a tape along the front edge for the length, then measure the front-to-back width at several points and average them. Area = length × average width — the averaging already accounts for the in-and-out of the curve, so no extra percentage is needed.

No. Measured by its average width, a curved border has the same area as a straight border of the same length and average width — a curve does not create extra ground area. Any percentage you add when ordering bark, compost or topsoil is a wastage/spillage allowance, not extra bed area.

Multiply the border area by the depth in metres. UK ornamental borders are usually mulched 50-75mm deep (0.05-0.075m), so a 12m² border at 50mm needs 12 × 0.05 = 0.6m³ (600 litres). Bark and compost are sold in litres, so add ~10% for settling when ordering bags.

Flexible steel, aluminium or recycled-plastic edging follows curves cleanly. Bricks or setts can be used but need cutting on tight radii. The calculator estimates the front-edge run as about 15% longer than the straight-line length to allow for the curve.

It is the run of edging you need around the open sides. For a straight or curved border set against a wall or lawn it is the front edge plus the two short returns; for a tapered (trapezium) bed it is the full perimeter — the two parallel ends plus the two sloping sides.