Frame Moulding Calculator — Total Length Needed

Because each rail runs from the inner sight edge out to the outer corner of the frame, every side is longer than the artwork by twice the moulding width. The standard framing rule is to take the artwork (rabbet) perimeter, multiply by two, then add eight times the moulding width — one width for each of the eight mitre faces. That total is exactly the outer perimeter of the finished frame, which is what this calculator returns. For 400 × 300 mm artwork with a 30 mm moulding: 2 × (400 + 300) = 1400 mm, plus 8 × 30 = 240 mm, giving 1640 mm (1.64 m).

The outer-perimeter figure is the bare length of moulding in the finished frame; it does not include saw kerf or test cuts. Framers typically buy about 10% over the perimeter to cover the kerf lost at each mitre and a spare cut or two. Tick "Include cutting allowance" to add this — for the 1.64 m example, 10% adds 0.16 m for a total of 1.80 m. Increase the allowance for very short rails, where the kerf is a larger share of each piece.

Yes, frame moulding in the UK is typically sold by the metre (or in fixed lengths of 2.4 m or 3 m). Some suppliers sell by the foot. Buy in whole lengths that each comfortably exceed your longest rail, and allow a little over the calculated total for mistakes.

Basic pine or obeche mouldings start around £2-4 per metre. Premium hardwood and ornate profiles can cost £10-30+ per metre. Aluminium section frames are another cost-effective option.