Why is the moulding length more than the artwork perimeter?

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).

How much extra moulding should I buy for waste?

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.

Is moulding sold by the metre?

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.

What is the cheapest frame moulding?

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.

Frame Moulding Calculator — Total Length Needed

Calculate the total length of moulding needed, with an optional cutting allowance.

Artwork Width

Visible artwork (sight) size — the moulding width is added automatically to reach the outer frame

Artwork Height

Visible artwork (sight) size, not the outer frame — enter the rabbet size if framing to fit a board exactly

Moulding ProfileSelect a moulding profile or enter custom dimensions

Number of Frames

How many identical frames to make from the same artwork size

Include cutting allowance

Add a percentage over the outer perimeter for saw kerf and trial cuts

Price per Metre (optional)

Supplier price per metre — leave blank to skip the cost estimate

How We Calculate This

Outer width = Artwork width + 2 × Moulding width

Outer height = Artwork height + 2 × Moulding width

Moulding length = 2 × (Outer width + Outer height)

Each 45° mitre runs the rail out to the outer corner, so the outer perimeter already includes the corner build-out for all eight mitre faces — this is the same as the classic "artwork perimeter + 8 × moulding width" rule. We do not add the eight widths a second time. A cutting allowance, if enabled, adds a percentage of the perimeter (default 10%) for saw kerf and trial cuts, then we multiply by the number of frames.

Frequently Asked Questions

Related Calculators

Frame Size Calculator

Calculate outer frame dimensions based on artwork size and moulding width. Includes rebate allowance and overall measurements.

Mat Board Calculator

Work out mat board dimensions and opening size with correct border widths. Includes weighted bottom border for professional results.

Glass Size Calculator

Calculate the glass or acrylic glazing size needed for your picture frame. Covers standard glass, non-reflective and UV-filtering.

Backing Board Calculator

Work out backing board dimensions and material needed for your picture frame. Covers MDF, foam core, corrugated board and acid-free options.

Mount Opening Calculator

Calculate mount opening dimensions with weighted bottom border and artwork overlap allowance for professional picture framing results.

Last updated: February 2026

All calculations are estimates. Always verify quantities before purchasing materials.