Two numbers are not enough. Almost every frame that has to be recut was ordered from a height and a width alone, and the recut is charged because the moulding has already been mitred.
Take four measurements. It takes two minutes.
1 and 2. Height and width of the whole piece
Measure the entire object, not the image. On a sheet of paper that means the full sheet including any unpainted margin. On a canvas it means the outer edge of the stretched canvas.
The common error is measuring the sight size, meaning only the part you can see, and ordering to that. The frame then has nothing to hold, because a rebate has to sit over the edge of the piece. Sight size is a useful number for designing a mat, but it is not the number you order a frame from.
Measure in millimetres. Inches with fractions invite mistakes, and a framer works in millimetres anyway.
3. Depth
The measurement people forget, and the one that causes the most trouble.
On a stretched canvas, measure from the front surface to the back of the stretcher bar. Stretcher bars run anywhere from about 19 mm on a light gallery canvas to 50 mm or more on a deep one. The frame's rebate has to be deeper than that number, or the canvas stands out of the front of the frame.
On a work on paper the depth is the whole package: backing board, artwork, mat, and glazing together. It is less critical but it still has to fit.
4. Both diagonals
Measure corner to corner, one way, then the other. If the two numbers differ, the piece is not square.
This is normal. Stretcher bars go out of square with humidity and handling, and a canvas that is 4 mm wider at the bottom than the top is completely ordinary. A frame cut to a single width will not close on it.
If the diagonals differ by more than about 3 mm, tell your framer. It is fixable, usually by adjusting the corner keys to bring the stretcher back to square before the frame is cut, but it has to be known about first.
The two-minute routine
- Lay the piece flat, face up, on a clean surface. Do not measure it hanging on the wall.
- Width at the top, and again at the bottom. Write down the larger.
- Height at the left, and again at the right. Write down the larger.
- Depth at one corner.
- Both diagonals.
- Note which edge was the top, so the framer knows the orientation.
Always use the larger of a pair. A frame slightly too generous can be shimmed. A frame slightly too tight cannot be stretched.
Things that change the measurement
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A deckled or torn edge on handmade paper. Measure to the furthest extent of the deckle, and mention it, because it usually means a float mount rather than a mat. See framing works on paper.
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A signature in the margin. If it should stay visible, the mat cannot cover it, and that changes the window size.
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Paint over the edge of a canvas. If the painting continues around the sides, a conventional frame will hide it. That is usually a floater frame decision instead.
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An existing backing or mount. Measure what you actually have, including anything already attached to the back.
Then check the arithmetic
Once you have the four numbers, the frame and mat calculator turns them into every dimension you need: the mat window, the outer mat, the frame size to order, the glazing, and the total moulding run. It draws the result to scale so you can see the proportions before anything is cut.
Or send us the numbers and a photograph. We will do it, and if a measurement looks wrong we will ask before anything is mitred.
Measuring an irregular or oddly shaped canvas
Not every piece is a clean rectangle. Shaped canvases, a rounded top, an octagon, an irregular hand-cut edge, need a different approach than the four standard measurements above, because there is no single height and width that describes the object.
Start by finding the bounding rectangle: the smallest straight-edged rectangle that fully contains the shape. Measure that rectangle's height and width the normal way, at the widest and tallest points of the piece. This is the number a framer needs first, because it sets the outer size of stock the frame will be built from, even for a shaped opening.
Next, document the actual shape itself rather than describing it in words. A photograph taken square-on from directly in front of the piece, with a tape measure or a known object like a ruler laid alongside it for scale, is far more reliable than a verbal description, since "rounded top" can mean a dozen different curves. For a genuinely irregular or asymmetric edge, a paper or cardboard template traced directly from the piece is the most accurate method, and it is what a framer will often ask for before cutting a custom mat opening or rebate to match.
Depth still matters exactly as much as on a rectangular piece, measure it the same way described above, and note any point where the shape's profile changes thickness, since an irregular piece is more likely than a flat rectangle to vary in depth across its surface. Bring the piece in, or send the bounding measurements plus the photograph and template, and we will confirm the shape before anything is cut.
What is sight size?
The part of the artwork you can see once it is framed, meaning the full piece minus whatever the mat or rebate covers. It matters when you are designing the mat and when comparing framed pieces. It is not what you order a frame from.
My canvas is not square. Is something wrong with it?
Almost certainly not. Wood moves, and stretcher bars shift over time with humidity. A few millimetres out is normal on a canvas of any age. It is only a problem if nobody accounts for it before the frame is cut.
Should I measure with the old frame on?
No. Take the piece out, or ask us to. The old frame's rebate hides part of the artwork, so measuring the visible area through an existing frame gives you the sight size, which is the classic way to order a frame that is too small.
