on June 04, 2026
Measuring a picture frame sounds straightforward. In practice, there are three different measurements involved — and confusing them is the most common reason a frame doesn't fit the print it was bought for.
The Three Measurements
Frame size (also called aperture or opening size) is the inner opening of the frame — the space visible through the front of the frame. When a frame is labelled 30x40cm, this is the measurement being described. Your print should be this size to fit the frame without a mat, or slightly larger if it will sit behind a mat with the mat cutting down to show the image area.
Rebate size (also called rabbet size) is the inner cavity of the frame — the total space behind the front lip of the frame, including the rebate step. This is where the print, mat, backing board, and glass all sit. The rebate size is always slightly larger than the frame opening — typically 3–5mm larger on each side — to allow the components to sit in the frame without being seen from the front.
Overall frame size is the outer dimensions of the frame, including the frame profile itself. This is what determines how much wall space the frame occupies and is useful for planning arrangements and spacing.
How to Measure Your Print
To find the right frame, measure your print first — not the paper it's on. If the image is printed edge-to-edge with no white border, the print size is the paper size. If there's a white border around the image, decide whether you're framing to show the full paper (including the border) or just the image area.
For framing with a mat: measure the image area (inside the white border). The mat opening will be cut to this size, and the frame needs to be large enough to accommodate both the image area and the mat border.
For framing without a mat: measure the full paper size. The frame opening should match this measurement exactly.
Measuring an Existing Frame
To find the frame size of a frame you already own: measure the inner opening from inside edge to inside edge on both dimensions. This is the size print it will hold without a mat.
To measure the rebate: open the frame backing and measure the inner cavity from the rebate step — this tells you the total space available for your print, mat, and backing board.
Tolerances
Frames and prints are manufactured to tolerances of 1–2mm. A print described as A4 (21x29.7cm) may measure 20.8x29.5cm when delivered. Allow for this variation when ordering — a frame with an opening of exactly 21x29.7cm will accommodate a print within this tolerance. A frame significantly smaller will not.
A Practical Approach
Measure your print before buying a frame. Write down both dimensions. Buy a frame with an opening that matches those dimensions. If you're framing with a mat, add twice your intended mat border width to each dimension to find the minimum frame size needed.
Browse ONE MAAY's full picture frame collection across all standard sizes.
