How to Measure for Custom Frames: Getting the Right Size Every Time

Measure the artwork edge-to-edge at its exact width and height, record it to the nearest 1/16 inch, and enter that as your art size unless a mat is involved — then measure the mat’s window opening instead.

One wrong number on a custom frame order and you’re out the cost of a non-returnable piece of millwork. A tape measure held crooked for a second, a mat’s hidden overlap, or a decorative outer edge mistaken for the opening — any of these sends the wrong figure to the frame maker, and the frame arrives a quarter-inch too tight for the print you were protecting.

The fix is a ten-minute measuring routine done at a flat table with the right conventions. Get the opening right, and the artwork drops in clean, the mat sits flush, and nothing gets clipped at the edges. This covers exactly what to measure, what to ignore, and the traps that cause most reframes.

What To Measure Depends On How You’re Framing

The dimension you enter is not always the artwork’s edge — it changes the moment a mat enters the picture. American Frame’s measuring guide puts it plainly: if you’re framing the art without a mat, measure the artwork itself; if you’re using a mat, measure the mat’s window opening instead of the full mat board.

Each convention exists for a reason. Without a mat, the frame’s rabbet — the inner ledge the art and backing rest against — must match the art’s exact dimensions, so the artwork is your measurement. With a mat, the mat window is what the viewer sees through, and the mat board itself sits behind the frame lip. Sizing from the full mat would leave you with an opening that swallows your image.

• No mat: measure the artwork edge-to-edge, width and height.
• With a mat: measure the mat’s window opening — the visible cutout, not the outer board.
• Reusing an existing frame: flip it over and measure the rabbet or internal opening, never the outside edges or the decorative face.

Some suppliers build in their own margins, so the safest habit is to check your framing service’s sizing rules before you start and follow their convention — because a number that’s right for one vendor can be wrong for the next.

Measuring Width And Height Accurately

Measure width left to right and height top to bottom, keeping the tape or ruler parallel to the edges and starting from the zero mark rather than the metal hook’s tip. Framing vendors recommend a rigid ruler or tape measure and recording every figure to the nearest 1/16 inch — not rounded to the nearest half or quarter.

Precision matters because frame makers cut to the number you submit. A sixteenth of an inch is the difference between a print that lies flat and one that buckles. EasyFrame’s measuring advice also notes that millimeters can be used for extra accuracy, and some custom builders take inside dimensions in millimeters — fractional inches like 11 3/16 × 14 1/2 are equally valid where the order form expects inches.

Take each measurement twice, from opposite ends, and trust the matching figure. If the two readings disagree, your tape drifted off-parallel and one of them is wrong.

Common Mistakes That Send The Wrong Number

The most expensive measuring errors come from measuring the wrong part of a frame or assuming a manufacturer’s allowance is zero. Web Picture Frames’ custom sizes guide stresses that you should follow the framing service’s own rules for art size, mat opening, and frame size, because some builders apply allowances automatically and others leave the subtracting to you.

Standard mats are a common surprise. Many apply a 1/8 inch overlap on all sides of the opening unless you switch it off, and multi-opening mat designers often expect you to size each opening 1/8 inch smaller on every side yourself. Frame lips are the other quiet offender: the inner lip of a frame can cover roughly 2–3 mm of a print’s outer edges, so any signature, caption, or detail sitting near the border risks disappearing behind the frame.

• Rounding 11 3/16 up to 11 1/4 — the frame arrives too loose.
• Measuring the outer frame edge instead of the rabbet.
• Including a white border you actually want the frame to hide.
• Assuming a square frame’s opening matches on both sides.
• Trusting one diagonal reading instead of two edge-aligned ones.

When you’ve got your numbers, our tested roundup of custom frames can point you to options that build in the tolerances you need.

Getting The Right Size Every Time

Work through these steps in order, and the measurement you submit will match the frame that arrives.

1. Decide on a mat. That single choice determines whether you measure art or window.
2. Lay the art flat on a table with the tape or ruler parallel to the edges.
3. Measure from left to right, then top to bottom, starting at the zero mark.
4. Repeat each measurement from the opposite end. If the readings disagree, retake both.
5. Record every figure to the nearest 1/16 inch — no rounding to the half or quarter.
6. Check your frame maker’s convention for mat overlap, frame lip, and inside versus finished size.
7. Keep signatures, text, and critical detail at least a few millimeters clear of the edges.
8. Order using the vendor’s units — fractional inches or millimeters — and confirm before you submit.

Write your final figures down twice and compare them before they go in the order form. The vendors’ own guidance is consistent on this point: the buyer is responsible for matching the service’s sizing rules, and a frame built to a measured opening never has to look generous to cover a mistake — it just fits.