Measure the artwork edge to edge at its widest width and tallest height, then record the size as width × height.
Ordering a custom frame starts with one number: the exact size of the piece you’re framing. Get it right and the process flows; get it wrong and you’re reordering glass and mat board. Measuring takes about two minutes with a rigid ruler and a flat surface.
Measure the Artwork, Not the Frame
The most common mistake is measuring the paper size or the outside of an old frame. Custom framers want the artwork’s exact visible size — the image area you want to show. Lay the artwork flat, gently flattening any curls, and use a rigid metal ruler for accuracy to 1/16 inch. Record the numbers in width × height format and enter that exact size into the frame builder.
Two details people overlook:
- Printed borders. If a white border or printed edge should be visible, include it; if not, measure only the image area.
- Signatures. If a signature should appear in the frame, include it in the measured size.
Don’t add extra allowance for the frame itself. The framer expects the exact art size — adding extra is how pieces come back misaligned.
Measuring With a Mat: What Changes
When a mat is part of the design, measure the area you want visible through the mat opening — not the full sheet size. Mixing these up hides part of the image. Framing guides from American Frame and Frame USA agree: the mat opening should sit slightly inside the artwork’s edge.
That’s a starting point, not a rule — personal taste and wall space matter.
Sizing an Existing Frame or Replacement Glass
If you already own a frame and want a new insert, custom mat, or replacement glass, flip the measuring logic. Remove the backing and measure the inside edge to inside edge of the backing board or frame opening — never the outside edges. The key term is rabbet opening, the inner ledge the artwork rests against.
| Situation | What to Measure | Why It Matters |
|---|---|---|
| New frame, no mat | Full artwork edge to edge | Framers expect the exact art size |
| New frame, with mat | Visible area through mat opening | Mat covers edges by ~2.5 mm per side |
| Existing frame | Inside opening / rabbet edge to edge | Outside edges give a wrong size |
| Canvas or thick art | Depth front to back, plus width × height | Frame rabbet must be deeper than the art |
For canvas or shadowbox pieces, measure the depth from the front surface to the back, including stretcher bars, cradle, or mounting hardware. The frame needs a rabbet deeper than that number, or the artwork won’t sit flat. American Frame’s measuring guide walks through the full process with diagrams.
Common Measuring Mistakes to Avoid
Even careful people slip on these four:
- Measuring the frame’s outside. Always the inside opening for an existing frame.
- Measuring paper size instead of the visible image. Borders and trim change the number.
- Adding extra allowance. Enter the exact art size; the framer adds the rest.
- Forgetting depth. Thick pieces need a deeper rabbet.
For irregularly cut or slightly non-square pieces, measure at the widest and tallest points and note the variance in the order form. Once you have your numbers, browsing our picks for the best custom picture frames online gives you a head start on where to order. Most frame designers accept inches, centimeters, or millimeters.
FAQs
What unit should I use when measuring artwork?
Inches with 1/16-inch precision is standard for most US framers, but centimeters and millimeters work too if you prefer metric. Most online frame designers accept all three. Just stay consistent — don’t mix inches and centimeters in the same order.
Should I measure the artwork or the mat when ordering a custom frame?
Measure the artwork’s visible area — what you want the viewer to see. If a mat is included, measure the image area shown through the opening. If no mat, measure the full artwork edge to edge. The framer’s designer will guide you from there.
What if my measurement falls between standard frame sizes?
Order a custom size rather than forcing the art into a stock frame. Round your measurement up to the nearest 1/8 inch and enter that into the frame builder. The slight extra space is invisible once the artwork is mounted.
References & Sources
- American Frame. “How to Measure Artwork.” Covers edge-to-edge measurement, mat openings, and precision standards.
- Frame USA. “Measuring Picture Frames and Mats.” Details rabbit openings and inside-dimension measuring for existing frames.
- Frame USA. “Picture Frame Sizes.” Explains standard sizing conventions and mat border guidelines.