Formula
Perimeter (ft) = 2 × (length + width). Pieces = perimeter in inches ÷ piece length, rounded up. Example: a 20 ft × 10 ft bed has a 60 ft perimeter; at 24-inch pieces that is 30 pieces, 32 with 5% spare.
How to use it, step by step
Measure the bed's length and width in feet, including any part you want edged — if one side is against a wall or path and needs no edging, subtract that side from the perimeter instead of using the full rectangle. Enter the length of one edging piece in inches from the product label. The calculator gives pieces needed plus a 5% spare allowance; order the spare, because cutting edging to fit corners always wastes some.
Worked example in detail
A 12 ft × 4 ft bed has perimeter 2 × (12 + 4) = 32 ft, or 384 inches. At 24-inch pieces, that is exactly 16 pieces, 17 with spare. At 12-inch pieces, it is 32 pieces, 34 with spare. Smaller pieces mean more joints and more cutting, so longer pieces are usually faster to install even if they cost more per piece.
What affects real edging needs
Corners, curves and level changes all increase waste. Rigid edging needs more cuts on curves than flexible edging. A bed on a slope needs edging stepped or cut to follow the ground. Always check the piece length on the actual product — '2 ft' edging is often slightly under 24 inches once the joining overlap is counted, so measure one piece rather than trusting the label alone.
Frequently asked questions
Should I edge all four sides?
Usually yes for a freestanding bed, to keep soil in and grass out. Against a wall or path, the wall does the job on that side, so do not pay to edge it.
What is edging for, exactly?
It holds soil and mulch inside the bed, stops grass creeping in, and gives a clean line for mowing. It does not replace weeding — weeds still grow inside the bed.
How deep should edging go?
Deep enough to stay put and block grass roots, usually 4–6 inches below the surface for lawn edging. Follow the product instructions for your edging type.