Tool
Frame & Mount Calculator
Enter your artwork size and border widths to get the aperture, mount and frame size - with optional weighted bottom border.
To size a mount, add the border width on each side to your visible image size. The mount board must be that size, the aperture is the visible image minus the overlap, and the frame is the mount size plus the width of the moulding. This calculator does the sums for you.
Defaults are in the units above. If you change units, enter your own values - typical borders are 50-100 mm (2-4 in).
Frames that fit your aperture with at least a 20 mm (¾ in) border, and the border each would give you.
How to calculate a mount and frame size
- Choose your units. Pick millimetres, centimetres or inches.
- Enter the visible image size. This is the aperture, the part of the drawing you want to show, plus how much the mount should overlap the paper edge.
- Set the mount border. Enter the border width for the top and sides. Add a weighted bottom border of 10, 15 or 20 percent if you want the classic gallery look.
- Enter the frame moulding width. Use the width of the visible face of the frame.
- Read the result. You get the mount board size, the aperture to cut and the outer frame size, plus the nearest standard frame.
How the calculation works
A mounted drawing is three nested rectangles: the aperture (what the viewer sees), the mount board (aperture plus borders) and the frame (mount board plus the moulding face). The calculator adds them in that order.
- Mount width = aperture width + 2 × side border.
- Mount height = aperture height + top border + bottom border.
- Frame outer size = mount size + 2 × moulding width.
- Minimum sheet size = aperture + 2 × overlap, so the mount can hold the drawing.
Choosing borders
Generous borders make a drawing feel valued and give it room to breathe; tight borders feel modern but can crowd detailed work. A bottom border slightly deeper than the top is a long-standing convention that keeps a picture visually settled. Use the standard-frame table to see what border a common frame size will give your drawing before you buy.
Frequently asked questions
What is the aperture?+
The aperture is the window cut in the mount board - the part of the artwork you see. It is slightly smaller than the sheet so the mount overlaps the edges and holds the drawing in place.
How much should the mount overlap the artwork?+
A typical overlap is 5 to 10 mm (about 1/4 inch) on each side, so the sheet must be at least that much larger than the aperture. Larger overlaps hide uneven edges.
What is a weighted bottom border?+
A slightly deeper bottom border than top - commonly 10 to 20 percent more - which stops the artwork looking as though it is sliding down inside the mount.
Are standard frame sizes the same everywhere?+
Not exactly. UK and European frames are usually metric (A-sizes or cm), while US frames are inch-based. Always measure your own frame's inner (rebate) size before cutting a mount.
How big should a mount border be?+
Borders between 5 and 8 cm (2 to 3 in) suit most drawings. Small drawings can take proportionally wider borders, which makes them feel more important.
What size frame do I need for an A4 drawing?+
An A4 drawing (210 x 297 mm) in a mount needs a bigger frame, commonly A3 for a generous border. Enter your sizes to see the exact result.
How much of my drawing should the mount cover?+
Overlap the paper edge by about 5 to 6 mm (a quarter of an inch) on each side so the paper is held securely and the edges stay hidden.