How to Measure Artwork for a Custom Picture Mount
A framer's step-by-step guide to measuring artwork for a made-to-measure picture mount — image area, aperture overlap and border sizes, so it fits first time.
A custom mount only looks right if the numbers behind it are right. Cut the window a millimetre too big and the artwork slips; cut it too small and you lose part of the image. Because we cut every mount to order on our computerised bevel cutter, the measurements you give us are exactly what we cut — so it's worth five minutes getting them right. Here's how we measure a piece for a made-to-measure mount at our Elephant & Castle bench.
What a window mount does
A window mount (or mat) is the card border that sits between your artwork and the frame. It isn't only decoration: it lifts the glass off the surface of the work so the two never touch, gives the eye somewhere to rest, and — in conservation-grade, acid-free board — protects the piece for decades. The aperture is the window cut through it; the border is the margin around that window.
What you'll need
- Your artwork, on a clean flat surface.
- A ruler or tape measure marked in millimetres — mm matter here.
- A pencil and a scrap of paper for your numbers.
Step 1 — Measure your artwork
Measure the full height and width of the artwork, then measure the image area — the part you actually want to show — if it's smaller than the sheet. Write both down in millimetres. Measure twice: paper is rarely a perfectly round number, and 2–3mm is the difference between a snug mount and a sloppy one.
Step 2 — Set the aperture (and the all-important overlap)
The window is cut slightly smaller than the image area so the mount overlaps the edges and holds the work in place — otherwise it drops straight through. We take about 3–4mm off each side. So if your image area is 200 × 250mm, the aperture is roughly 192 × 242mm.
If your artwork has an edge you want to keep — a signature, a deckled edge, a plate mark — measure to include it and tell us; we can float the work or cut the window wider to show it.
Step 3 — Choose your borders
The border is the visible band of mount around the window. Wider borders look calmer and more gallery-like; 50–80mm (5–8cm) suits most pieces, and small works often benefit from proportionally more. Keep the left, right and top equal.
One framer's convention worth knowing: make the bottom border a touch deeper than the other three — a “deeper base”. It counters an optical illusion that makes an evenly-bordered mount look bottom-heavy, and it's the traditional look for fine art. The outer size of the mount is simply your aperture plus the borders on each side.
How a window mount goes together
The finished mount sits on top of the artwork, which is hinged to a backing board behind it; the whole sandwich then goes into the frame. Seeing it laid out makes the overlap obvious — the cream border frames the image, and the bevelled window edge catches the light.
Ordering your custom mount
Once you have three numbers — image area, aperture (image minus the overlap) and outer size (aperture plus borders) — you're ready to order. Put them into our custom window mount, cut to size, or browse the full picture mounts range. Every mount is cut from conservation-grade, acid-free board on a computerised bevel cutter, so what you measure is what you get. Not sure on standard print and frame dimensions? Our print, paper & frame sizes guide lists them all.
Common mistakes
- Measuring the sheet, not the image. If there's white space you don't want on show, measure the image area.
- Forgetting the overlap. The aperture must be smaller than the image, or the work falls through.
- Working in whole centimetres. Round numbers hide 2–3mm errors — measure to the millimetre.
- Even borders on fine art. A slightly deeper base usually looks more balanced.
Prefer to leave it to us?
Bring the piece into the shop and we'll measure it, advise on border and colour, and cut it while you browse — or have it done as part of full bespoke framing. And once it's mounted and framed, our guide to hanging a picture properly takes it the rest of the way to the wall.
Frequently asked questions
How much smaller than the artwork should the mount aperture be?
About 3–4mm smaller on each side of the image area, so the mount overlaps the edges and holds the work without it slipping through.
What size border should a picture mount have?
50–80mm (5–8cm) suits most pieces; smaller works often look best with proportionally wider borders. Keep the sides and top equal, and make the bottom slightly deeper.
What measurements do you need to cut a custom mount?
Three: the image area you want to show, the aperture (image minus a 3–4mm overlap each side) and the outer size (aperture plus your chosen borders). All in millimetres.
Should I measure the paper or the image?
Measure both, but the aperture is set from the image area — the part you want visible. Tell us if you want to keep a border, signature or deckled edge on show.