Canvas Size Calculator

Picking a canvas is two decisions wearing one hat: how big, and what shape. This calculator answers the first from the size of the thing you are painting, and the second from the aspect ratio you choose.

How big. The subject should not fill the canvas. It needs room to sit in, and a workable default is to let it occupy about 65% of the canvas in whichever dimension runs out first. That leaves a sixth of the canvas as breathing space on each side.

Canvas dimension = Subject dimension ÷ 0.65

Treat 65% as a starting point rather than a rule. Portrait heads are often cropped tighter than that, still lifes and landscapes usually want more air, and a deliberately claustrophobic composition breaks the guideline on purpose.

What shape. The ratio then stretches whichever dimension falls short of it. The calculator only ever grows the canvas, never shrinks it, so the subject always fits.

Orientation follows the subject. A 2:3 ratio means a tall canvas for a tall subject and a wide one for a wide subject. It is the same rectangle turned ninety degrees, and stretcher bars do not care which way round you hang them.

Standard stretcher sizes in inches, all sold in either orientation: 8×10, 9×12, 11×14, 12×16, 16×20, 18×24, 20×24, 24×30, 24×36, 30×40, 36×48, 48×60, plus the squares: 8×8, 12×12, 16×16, 20×20, 24×24, 30×30, 36×36.

Past about 24 inches on the long side, add a crossbar brace. Stretcher bars bow inward under canvas tension, and on a 36-inch span that bow is visible from across the room.

Worked example A 12 × 16 inch subject at 4:5.

• From the subject: 12 ÷ 0.65 = 18.5 wide, 16 ÷ 0.65 = 24.6 tall
• Grown to 4:5: 24.6 × 4/5 = 19.7 wide, so the ideal is 19.7 × 24.6 inches
• Nearest standard that fits: 20 × 24 inches
• The subject then covers about 40% of the canvas by area

Where the standard sizes let you down Anything wider than roughly 3:2 has no off-the-shelf equivalent. The common range runs from square to 3:4, with 24×36 at 2:3 as the widest ordinary size, so a genuine panorama means a custom bar set or cutting your own. The result panel says so when the nearest standard is a poor match for the ratio you asked for, instead of quietly handing you the wrong shape.

If you are printing rather than painting Print size and pixel count are tied together by resolution: print inches = pixels ÷ DPI. At 300 DPI a 4,000 × 6,000 pixel photo prints sharp up to 13.3 × 20 inches. Posters seen from three feet are fine at 150 DPI, and large-format work viewed from ten feet holds up at 72 to 100. Going the other way, a 16 × 20 canvas print at 300 DPI wants 4,800 × 6,000 pixels, which is 28.8 megapixels.