Free Canvas Size Calculator

Stretched canvases are sold in a set of sizes inherited from framing and from imperial paper conventions: 8×10, 9×12, 11×14, 16×20, 18×24, 24×36 and so on. They exist because ready-made frames exist in the same dimensions, and because stretcher bars are manufactured in inch increments.

A full-frame or APS-C camera produces 3:2, inherited from 35mm film. Micro Four Thirds and most phone cameras produce 4:3. Neither is a common canvas ratio in the small and medium sizes, which is where most painting happens.

A 3:2 photograph on a 16×20 canvas — a 4:5 ratio — loses about 17% of its width. On an 8×10, the same. That is not a rounding error: it is a sixth of the frame, and where it comes from decides whether the painting works.

This is why the crop percentage is the useful output. A number tells you whether you are trimming a margin or removing a third of the composition, and it does so before the canvas is bought rather than after.

The first question is whether the crop is at the edges or through the subject. A landscape photograph with expendable sky and foreground survives a 17% loss off the top and bottom, and frequently improves. A portrait framed tightly has nothing spare, and the same crop takes the top of the head.

The second is whether the composition depends on its proportions. A picture built on the diagonal of a 3:2 rectangle stops working when the rectangle changes shape, because the diagonal moves. A centrally composed subject is far more tolerant.

The third is whether to change orientation deliberately. A landscape photograph cropped to an upright canvas loses a great deal, and sometimes the result is stronger — the crop forces a decision about what the subject actually is. Forcing portrait in the calculator shows what that costs.

There is an alternative to cropping: paint the reference at its own proportion inside a larger canvas, leaving a margin. On a stretched canvas that margin usually becomes part of the work — a painted border, a field of colour, or bare primed surface.

It is a legitimate choice and it removes the crop problem entirely, at the cost of buying a canvas larger than the image. The calculator's exact-fit entries are the alternative to it, which is why they are labelled rather than ranked silently.

The aspect ratio calculator reduces a pair of numbers to its simplest ratio, and the 3:2 rectangle generator draws the armature of the commonest camera proportion. Square canvases have become far more common than they were, largely because square is the one ratio that crops symmetrically from any source. A 3:2 landscape and a 2:3 portrait lose the same proportion to a square, from opposite axes.

That symmetry is also why a square is a demanding composition. Nothing in the frame is favoured by the shape, so there is no natural direction and the picture has to supply its own. Photographers who shoot square deliberately do it for exactly that reason.

Stretched canvases come in different depths — commonly around 1.8 cm for a standard profile and 3.8 cm or more for a gallery or deep-edge profile. The face dimensions are the same, but a deep-edge canvas wraps the image around the sides if you paint them.

If you intend to paint the edges, the effective face is smaller than the stated size, and anything important near the border wraps out of the front view. It is not part of the ratio arithmetic, and it is the commonest surprise after the crop.

Stretched canvas is not the only surface with fixed dimensions. Cradled wood panels follow much the same imperial set, because they are sold into the same frames. Canvas boards and canvas pads tend to run smaller and cheaper, which makes them the sensible surface for testing a crop before committing to a stretched canvas.

Watercolour and printmaking papers follow different conventions entirely. Full imperial sheets are 22 by 30 inches, a ratio close to 3:4, and half and quarter sheets inherit it by folding. That means paper work and canvas work often want different crops of the same reference, which is worth knowing before a single decision is made for both.

Panels also behave differently at large sizes. Above about 30 inches a stretched canvas needs a cross brace to stay flat, while a cradled panel does not, and that structural difference sometimes decides the surface before the proportion does.

Enter the dimensions of the file or print you are going to work from, not the dimensions of the original scene or an earlier version. A photograph already cropped in an editor has a different ratio from the one the camera produced, and it is the cropped version that is going onto the canvas.

Take the reference proportion from the file itself rather than from memory. Then decide whether the composition can survive a crop and roughly how much. Then look at the list, which is already ordered by that criterion, and take the largest size in the acceptable band — bigger canvases are easier to paint on than smaller ones, and the crop percentage does not change with size, only with ratio.

The sizes at the top of the list are all the same ratio, so choosing among them is purely a question of how large you want to work and what you are willing to carry home. The dynamic symmetry overlays treat several of these as constructions in their own right, and the root 2 rectangle overlay is the one the paper sizes are built on.