Frame Size Calculator
Determine the correct frame size for your artwork with mat borders and moulding.
Frame Preview
Closest Standard Frame Sizes
How to Use This Calculator
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1
Measure your artwork
Measure the visible area of your art piece. This is the width and height of the image or print that you want to display within the frame.
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2
Set mat borders
Choose uniform mat borders for equal spacing on all sides, or switch to custom mode to set different widths for top, bottom, left, and right. A slightly larger bottom border is traditional for visual balance.
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3
Add frame moulding
Enter the width of your frame moulding profile. This is the visible border of the frame itself around the mat. Typical moulding widths are 15-40mm.
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4
Read frame size
The calculator shows the required frame inner dimensions (glass/backing size). This is the size you need when shopping for a frame. The overall outer size includes the moulding width.
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5
Check standard sizes
See which off-the-shelf standard frame sizes are closest to your requirements. If a close match exists, you may be able to adjust the mat borders slightly to fit a standard frame and save on custom framing costs.
Frame, Mat, and Moulding: How the Sizes Fit Together
Buying a frame for an existing artwork is a small geometry problem with traps in it. The number on a shop frame is its inner size — the size of artwork or mat it accepts — not its outer dimensions on the wall. Add a mat and the artwork no longer matches the frame size at all; add wide moulding and the wall footprint grows well beyond what you planned. This calculator works through the chain — artwork → mat opening → mat outer size → frame inner size → overall outer size — in either direction, so you can start from the art you own or the wall space you have.
The mat opening overlap
A mat's window must be slightly smaller than the artwork, so the mat overlaps the art's edges and holds it flat. The standard overlap is 3–5mm per side. For a 300×400mm print, a 294×394mm opening (3mm overlap each side) is typical. Skip the overlap and the artwork falls through; overdo it and you crop the image. If the art has a printed border or signature near the edge, check the overlap won't swallow it — pencil signatures on prints traditionally stay visible.
How wide should the mat be?
Wider than you think. Narrow mats (under 40mm) tend to look like an apology; generous mats give the artwork room to breathe and make inexpensive prints look considered. Useful starting points:
- Small art (under A4): 50–65mm borders
- Medium art (A4–A2): 65–90mm borders
- Large art (A2+): 90–120mm borders
- Weighted bottom: making the bottom border 10–20% deeper than the others counteracts the optical illusion that centred art sits low. Traditional, optional, and most visible on portrait-orientation pieces.
A worked example
Artwork: 297×420mm (A3) print. Mat: 70mm borders, 3mm overlap per side. Moulding: 25mm wide.
Mat opening = 291×414mm. Mat outer size (= frame inner size) = 291 + 140 = 431mm wide, 414 + 140 = 554mm tall. The frame you need to buy is therefore a 431×554mm (inner) frame — in practice the nearest stock size is 40×50cm-ish territory, so you'd either trim the mat borders to fit a 400×500mm stock frame or order a custom one. On the wall, the overall footprint is 431 + 50 = 481mm × 604mm including the 25mm moulding all round.
Stock sizes versus custom framing
Stock frames cost a fraction of custom ones, and the calculator makes it easy to work backwards from a stock size: enter the frame's inner dimensions and your artwork size, and see what mat borders result. Borders within about 10mm of each other on width and height look intentional; wildly unequal borders (say 40mm sides, 95mm top) look like a mistake — at that point, pay for a custom mat (cheap) inside a stock frame rather than a fully custom frame (expensive).
Standard sizes cheat sheet
| Paper / print | Size (mm) | Common stock frame pairing |
|---|---|---|
| A4 | 210 × 297 | 300 × 400 frame with ~45/50mm mat |
| A3 | 297 × 420 | 400 × 500 frame with ~40/50mm mat |
| A2 | 420 × 594 | 500 × 700 frame with ~40/53mm mat |
| 8×10 in | 203 × 254 | 11×14 in frame with ~2 in mat |
| Square print | 300 × 300 | 400 × 400 frame with 50mm mat |
Don't forget the glazing and depth
Frame depth (rebate) matters for canvases and thick artwork: a stretched canvas needs a deep rebate or a floater frame, not a standard picture frame. And once the framed piece is assembled, its outer size is what you'll feed into our hanging calculators — the main calculator for placement and the Wire Length Calculator if you're fitting the hanging hardware yourself.
Frequently Asked Questions
Is a shop frame's stated size the inner or outer measurement?
Inner — a "40 × 50cm" frame accepts a 40×50cm mat or artwork. Its outer size is bigger by twice the moulding width in each direction. The calculator reports both so you can check the wall footprint, which is the number that matters for placement.
Can I frame without a mat?
Yes — the artwork then needs to match the frame's inner size exactly, and the art touches the glazing, which is fine for posters and replaceable prints but not recommended for valuable or original work (trapped moisture and sticking are the risks). Set the mat borders to zero in the calculator for this case.
What's the difference between a mat and a mount?
Nothing — "mat" (or matboard) is the US term, "mount" the UK one, for the same window-cut board. This site uses mat for consistency. Either way, choose acid-free board for anything you care about; standard board yellows and can damage art over years.
My artwork is an odd size. Trim the art or pay for custom?
Never trim original art or limited prints — the mat absorbs the size mismatch instead. Enter your art size and a stock frame's inner size into the calculator and see what borders result; if they're unbalanced, a framer can cut a custom mat for a stock frame, which costs far less than full custom framing.
What is mat overlap?
Mats typically overlap the artwork by 3-6mm on each side to hold it in place. This means the visible opening of the mat is slightly smaller than the full artwork dimensions. The overlap ensures the art stays securely behind the mat without slipping. This calculator accounts for a standard 3mm overlap on each side when showing the mat opening size.
How do I choose mat border width?
Standard mat border width is 50-75mm (2-3 inches). The bottom border is often made 10-15mm larger than the top for visual balance, as equal borders can make the bottom appear narrower due to an optical illusion. Larger artworks generally benefit from wider mat borders, while very small pieces may look best with proportionally generous borders.
What if no standard frame size fits my artwork?
If no standard frame size matches, you have a few options. Consider custom framing for a perfect fit. Alternatively, adjust your mat border widths to accommodate the nearest standard frame size. You can also look for oversized standard frames and use wider mat borders to fill the extra space, which can actually enhance the presentation.