ArtCalcs.uk
Backing Board Calculator — Size & Material
Work out backing board size and material needed for your frame.
How We Calculate This
Backing board = Rebate size − Clearance (total)
The backing board sits behind the artwork and mount/mat at the very rear of the frame, secured with framer's points, brads or turn buttons. It is cut a little smaller than the frame's rear aperture (the rebate) so it drops in without jamming and leaves room for the materials to expand and contract — a total clearance of 1–3 mm is standard (UK framers typically work to ~3 mm; this defaults to 2 mm).
Weight is estimated from the cut area and the board's areal mass: MDF (3 mm) ≈ 2250 g/m², greyboard (2 mm) ≈ 1500 g/m², corrugated plastic (4 mm Correx) ≈ 700 g/m² and foam core (5 mm) ≈ 290 g/m². Sandwich boards are quoted by sheet weight, not bulk density, so this reflects real supplier figures.
Frequently Asked Questions
MDF is sturdy and moisture-resistant, ideal for larger frames. Foam core is lightweight but less rigid. Greyboard is affordable and acid-free options are available for conservation framing. Corrugated plastic is waterproof and strong.
For valuable or archival work, yes. Acid-free backing prevents yellowing and deterioration of the artwork over time. Standard MDF and cardboard can off-gas acids that damage paper-based works.
Standard backing is 2-3 mm. For larger frames (over 500 mm), use 3-4 mm for rigidity. Foam core at 5 mm provides good rigidity with light weight, ideal for large frames and shipping.
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Last updated: February 2026
All calculations are estimates. Always verify quantities before purchasing materials.