Before anything else: measure the blank margin around the printed image. If it is less than about an inch and a half, your canvas cannot be stretched over bars, and no technique will change that.
This is the single most useful thing on this page and most guides skip it entirely. Plenty of unframed paint by numbers canvases — including our own — are trimmed close to the printed edge to keep the cost down. There is simply not enough spare material to wrap around a stretcher bar and staple to the back. Trying anyway means either stapling through your painting or pulling the printed image around the edge where you cannot see it.
So start with a ruler, not a staple gun.
The margin test
Lay the canvas flat and measure from the edge of the printed design to the cut edge of the fabric, on all four sides.
- Two inches or more: you can stretch it. Skip to the stretching section below.
- An inch and a half: possible over slim bars, with no room for error and nothing to grip when you pull. Not enjoyable.
- Less than an inch and a half: do not stretch it. The options below are better and none of them risks the painting.
Our unframed 16x20 falls into the last category, which is why we say on every product page that it suits mounting to a board rather than stretching over a frame. If you want a canvas that arrives ready to hang, the framed sizes come pre-stretched on a wooden frame and there is nothing to do at all.
If the margin is too small
Three good options, cheapest first.
Mount it to a board
The most common answer and the one most people are happiest with. Cut a piece of foam board, mat board or thin plywood to the size of the printed image. Attach the canvas to it with acid-free double-sided tape or a spray adhesive rated for artwork, working from the center outward to push out air as you go. Trim the surplus flush at the back.
Do this before painting if you can. A canvas taped to a board is far more pleasant to paint on than a loose one, which moves under the brush.
Put it in a frame with a mat
A standard off-the-shelf frame in a common size, with a mat cut to overlap the printed edge by an eighth of an inch or so. The mat hides the cut edge and holds the canvas flat, and the whole job costs very little. Note that acrylic paint has texture, so avoid pressing glass directly against the surface — either use a mat deep enough to keep it clear, or leave the glass out.
Take it to a framer
Worth it for something you spent thirty hours on. A framer can float-mount it, which shows the edges deliberately rather than hiding them, and that suits a hand-painted canvas well.
Our separate guide to framing a finished paint by number canvas goes through these in more detail.
If you do have the margin: stretching properly
This applies to a blank artist's canvas or a kit that shipped with stretcher bars.
1. Assemble the bars
Lay the stretcher bars out and check for warping or splits before you start. Clear any sawdust from the grooves with a dry brush, then slide the corners together by hand — a long bar with a short bar first, then the remaining two.
Tap the corners home with a rubber or wooden mallet, not a hammer, which will dent the wood. A scrap block between mallet and bar protects it further.
2. Check it is square, using the diagonals
Worth doing properly, because the obvious method does not work. Measuring that opposite sides are equal only proves you have a parallelogram — a frame leaning noticeably to one side passes that test.
Measure corner to corner, both ways. When the two diagonals are equal, the frame is square. If they are not, push gently on the longer diagonal until they match.
3. Lay the canvas face down
On a clean, clear surface. Center the frame on the back of the canvas, bevelled edge facing up and away from the fabric — the flat face of the bar goes against the canvas. The bevel is what stops the bar edge printing a line through the front.
Check the alignment against the printed image under good light before you fix anything.
4. Staple from the centers outward
This is the part people get wrong, and it is the difference between a taut canvas and a wrinkled one.
Put one staple in the middle of one long side. Go to the opposite side, pull the canvas taut, and staple its middle. Then the middle of each short side, again in opposing pairs. You now have four staples and the tension is balanced.
Work outward from those centers, always alternating opposite sides, spacing staples roughly two inches apart. Never work along one whole side and then start the next — that drags the weave sideways and puts a diagonal ripple across the finished piece that cannot be pulled out.
Leave the corners until last, fold them into a neat pleat, and staple down.
5. Check the front as you go
Flip it over every few staples. Thumbtacks pushed halfway in are useful here for a first attempt, since they come out easily if the alignment has drifted.
Creases, and what not to do
A canvas that has been folded arrives with hard creases, and the usual advice is to iron them out. Do not iron a printed paint by numbers canvas.
The printing sits on a primer layer, and heat plus pressure can soften it, mark it, or lift printed detail — which is unrecoverable, because the numbers are the whole product. An earlier version of this page recommended a high-heat setting, which is worse still.
What to do instead: lay the canvas flat under a stack of heavy books for several days. It will not remove a hard crease entirely, and nothing will. This is why the packing matters so much — our canvases ship rolled in a tube rather than folded, precisely so there is nothing to flatten. If you are buying elsewhere, it is the question worth asking first.
A note on building your own frame
Gluing scrap wood into a rectangle will not do this job. A stretcher bar has a bevelled inner edge so the wood does not print through the canvas, and a joint strong enough to resist the constant inward pull of stretched fabric. Glued butt joints in softwood come apart, and when they do the canvas goes slack.
Bare stretcher bars are inexpensive and sold in matched pairs by length. Buy them.
Common questions
Should I stretch the canvas before or after painting?
Before, if you can. A canvas already mounted on a board or bars is flat, stable and pleasant to paint on. A loose one shifts under the brush and is much harder to keep clean at the edges.
How much spare canvas do I need?
About two inches beyond the image on every side for a standard bar. That allows for the depth of the bar, the wrap onto the back, and enough left over to actually grip while you pull.
Can I use a hammer instead of a mallet?
A hammer dents the wood, and a dent in a stretcher bar can telegraph through as a mark on the canvas. If you only have a hammer, hit a scrap block rather than the frame.
If you would rather build the frame than buy one, making your own stretcher frame covers when that is worth doing and when it is not.
My canvas has gone slightly slack. Can I fix it?
A very light mist of water on the back only, then let it dry, will tighten cotton canvas as it shrinks. Use it sparingly, keep it off the front, and never do this on a printed canvas, where water can lift the numbers.
Is there a version that skips all of this?
Yes — the framed sizes of our kits arrive pre-stretched on a wooden frame and ready to hang the moment the paint dries.
