For a poster going into an existing frame, order the size of the paper the frame holds—not the frame’s outside dimensions. The moulding adds width and height that do not belong in your print measurement.
Where possible, remove the existing insert and measure it flat. Work in centimetres and record width first, then height. For an awkward dimension, 325 mm is 32.5 cm: divide millimetres by ten.
Is A3 the same as a 30 × 40 cm poster?
No. A3 is 29.7 × 42 cm: it is 3 mm narrower and 20 mm taller than a 30 × 40 cm sheet. Those are different paper sizes, even though they can look similar in a product photograph.
For a frame that takes a 30 × 40 cm insert, choose that sheet size where supported rather than ordering A3 and hoping it will fit. Measure any mount opening separately. Trimming a larger sheet can remove important picture detail and does not correct a sheet that is already too narrow.
Use the measured insert size when choosing your photo poster, then check the crop. A frame’s outside measurements or its brand name do not establish the print size it accepts.
A frame without a mount
Check the insert against the frame’s stated print size. If the insert is missing, the backing or internal recess can help you establish the intended size. Measure carefully and do not force glass or dismantle a fragile frame unnecessarily.
Some frames overlap the print slightly at its edges. That means a print that fits physically can still have a small amount of its image hidden. Keep essential lettering and faces away from that boundary.
A frame with a mount
A mount creates two separate measurements: the outer paper space and the visible opening. You need enough paper for the print to sit securely behind the opening; ordering exactly the opening size may leave no overlap to hold it.
For example, a frame may hold a 30 × 40 cm sheet while its mount reveals a smaller area. If you order a 30 × 40 cm photograph printed across the sheet, the mount can hide substantial parts of the picture. Plan which part should be visible before ordering. A white border is not automatically included just because a frame has a mount.
A worked measurement: sheet versus window
Hypothetical example, not a measurement of a particular frame: the frame accepts a 30 × 40cm sheet, while the mount opening is 20 × 30cm. The paper must fit the 30 × 40cm space. Ordering a 20 × 30cm sheet solely because of the visible window may leave too little paper to secure behind the mount.
A centred 20 × 30cm window within a 30 × 40cm sheet leaves 5cm of sheet around each side in this simple illustration. That describes the example geometry, not a universal mounting allowance. Real mounts can be off-centre, bevelled or asymmetric. Confirm how the print will be held and which image area must remain visible.
Measure in this order
- Identify the intended orientation and the frame’s stated paper size.
- Safely remove an existing insert and measure it flat, width then height. Compare the glass or backing only if it is safe to handle and actually represents the required fit.
- If there is no insert, inspect the internal recess and fittings. Ask the framer or manufacturer when the fit is uncertain; do not guess a clearance.
- Measure any mount opening separately and note whether it is centred.
- Plan the photograph within that visible area. Keep important faces and lettering away from the covered edges.
- Check the selected paper dimensions, units and crop in the creator before ordering.
For example, 325mm ÷ 10 = 32.5cm. A frame labelled in inches needs a proper unit conversion; do not enter the inch numbers into centimetre fields. Frames of the same brand can have different inserts, mounts and recesses, so an IKEA or other brand name is not a substitute for checking this particular frame.
Check the photograph’s proportions
Changing the paper dimensions can change the crop. After entering a custom size, inspect all four edges and confirm portrait or landscape orientation. Do not stretch the photograph to make it fit.
Write down the required paper size and, separately, any mount opening. If those measurements are uncertain, resolve them before placing the order. Explore custom-size poster printing and use the preview to check the photograph against the dimensions you need.
Enter the paper size, then check the preview
Start with the custom-size poster route. Enter the measured paper width and height in the selected units. The creator validates supported dimensions and quotes the price; a frame size is not a promise that every dimension can be produced. If your measurement is rejected or the crop cannot protect the visible image, ask the workshop before changing the size just to make the form accept it.
A mount does not automatically tell the creator to add a border. Supply a final file with any intended border or ask how to prepare it. The print preview shows the selected sheet, not a measured simulation of your mount. Compare it with the separate window measurement.
The current public poster size calculator, checked 9 October 2026, accepts custom dimensions from 14.732 × 20.955cm up to 99.06 × 152.4cm, comparing the shorter and longer sides regardless of orientation. Smaller named presets are exceptions: use the named size when it matches your frame. These are the published calculator limits, not a promise that an untested file or unusual mounting arrangement is suitable. Recheck the creator for your exact dimensions.
Frame-measurement questions
Should I measure the outside of the frame?
No. Measure the paper it is designed to hold. The outside includes moulding that does not belong in the sheet dimensions.
Is the mount opening the poster size?
Not usually. The paper continues behind the mount and must fit the frame. Record the paper size and the visible window separately.
How much overlap should I leave?
There is no single allowance for every frame and mounting method. Confirm the actual fit and fixing with the frame supplier or framer, and protect essential image details from the covered area.
Can I order a print for a branded frame?
Use the actual insert, recess and mount measurements. Do not assume that every frame from a particular brand shares one size or construction.
Does the poster include a frame?
No. YI2C photo posters are supplied unframed on 230gsm Fine Art Pure White Matt paper. Standard poster sizes include free delivery; custom posters over 140cm on the longest side currently carry a £12 delivery charge. Check the complete creator quote before ordering. The frame is a separate purchase.
