How this calculator works
A frame is sized from the outside in. Each picture needs a border of mat or mount around all four sides, and when several pictures sit in a row the openings are separated by a gap. The frame width is therefore the pictures plus the gaps plus the border on the left and right, and the frame height is one picture plus the border top and bottom. The moulding length is the perimeter of the outside of the frame, which is what a framer charges by, and the glass area is the outer opening, which is the size of the glass sheet. Rebates and the width of the moulding itself are not added here, so allow a few millimetres on each side when the framer cuts.
Formula
frame width = count x picture width + (count - 1) x gap + 2 x border. Frame height = picture height + 2 x border. Moulding length = 2 x (frame width + frame height). Glass area = frame width x frame height.
Worked example
One 20 cm by 25 cm print with a 5 cm border gives a 30 cm by 35 cm frame, 130 cm of moulding and 0.105 m2 of glass. Three 20 cm by 25 cm prints in a row with 4 cm gaps give a 20 x 3 + 4 x 2 + 10 = 78 cm wide frame and 35 cm high, 226 cm of moulding and 0.273 m2 of glass.
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Frequently asked questions
Does the frame size include the moulding width?
It is the outer opening the glass fills, not the outer edge of the frame. A 2 cm wide moulding adds 2 cm on every side, so a 30 by 35 cm opening needs a 34 by 39 cm outer frame.
How much border should a mat have?
A border of 5 cm to 8 cm suits most prints, with a slightly wider bottom edge in traditional framing. Small prints look better with a generous border, because a thin one makes the artwork feel cramped.
Should the glass area allow for the rebate?
The rebate, the lip the glass sits in, overlaps the glass by a few millimetres on each edge. Order the glass to the opening size and let the framer trim or allow for the lip.
What if my pictures are different sizes?
This calculator assumes a row of identical prints. For mixed sizes, work out the widest row by adding each picture and gap individually and use that width for the frame.