How to Stretch a Canvas for Painting — the Easy Way!

by Damian Osborne


As an artist, knowing how to stretch a canvas is important. Not only does it save you a lot of money. But by stretching and priming your own canvases, you’ll gain a better understanding of your materials, and the possible defects of painting in general.

You’ll also learn of the various options available regarding painting supports. And, by stretching your own canvas, you’ll be assured of the quality of the materials at each step, since you’re the one who decides what to use.

If you want to learn how to make and prime a rigid support for painting, check out Making Your Own Canvas Panels for Oil Painting.


Stretching a Belgian linen canvas on a strainer frame.


How to Stretch a Canvas for Painting

1. Lay out a length of your cotton duck or Belgian linen canvas roll on a clean surface.

2. Place a canvas stretcher or strainer frame with the beveled side down on the length of canvas.

3. With a sharp tailor’s scissors, cut the canvas around the support frame, ensuring that you cut straight, and allowing at least 2 inches/5 cm of extra canvas all around the frame.

4. Mark the midpoint on the inside of each bar of the stretcher/strainer with a pencil. Then mark a handbreadth (or less, depending on the size of your canvas) either side of the midpoint. Continue to mark handbreadths until you reach the ends of each bar of the frame.

5. Make sure the stretcher/strainer is placed in the very centre of the piece of canvas fabric. Starting with one of the long sides, fold the edge of the canvas over by an inch or so to double the edge. Then fold the doubled edge of the fabric over the bar of the stretcher/strainer frame.

6. Check that there is still enough extra canvas on each of the other three sides of the frame and that it all lines up square. Then staple or nail the double fold of canvas at the marked midpoint of the frame.

7. Now, at the opposite side, fold the canvas fabric to create a folded edge, then pull it as hard as you can against stapled/nailed side. You can use canvas pliers, or do it by hand.

8. Maintaining the pulled tension in the canvas, fold the doubled edge of the canvas over the bar of the frame and staple/nail it at the marked midpoint.

9. Continue to do the same at the midpoints of the other two sides, making sure you pull against the side that is already stapled/nailed so that the tension in the canvas is evenly distributed on all sides.

10. Once the canvas has been pinned at the midpoint of each bar of the frame, pull the canvas fabric as hard as you can at one of the 90° corners of the frame. Then fold the canvas fabric over the corner and temporarily nail it at the corner.

11. Pull the canvas and temporarily pin it at each of the other three corners, creating a diamond-like tension-fold.

12. Now, beginning with one of the long sides, pull the canvas toward the mark next to the midpoint. Maintain the doubled edge and the canvas tension, and fold over the bar of the frame. Staple or nail it at this marked point. 

13. Turn the frame like a wheel to the opposite side and in a mirroring fashion, pull the canvas, fold over and staple/nail it at the next marked point after the midpoint.

14. Continue to staple/nail the canvas fabric at opposite points each time so that you work from the midpoint outwards towards the corners. Maintain even tension across the canvas.

15. Once you’ve stretched the canvas and pinned it to every marked point, you should just have the corners still to do. Pull out the temporary corner pins and smooth out the canvas. Staple/nail the fabric at the last remaining marks near the corners of the frame, but leave enough space to allow you to fold in the corners of the fabric and finish it off.

16. Then at each corner, make a 90° cut in the fabric so that you are able fold the fabric edges in to make neat corner folds. 

17. Pull the canvas hard towards one of the corners of the frame, fold in the corners of the canvas fabric, fold over the frame, and staple/nail the fabric creating a neat corner. 

18. Do the same on the other three corners, working from the opposite side and corner. Check your canvas tension throughout. 

19. Your canvas is now stretched over the stretcher/strainer support frame and ready for sizing and priming. If you tap the canvas fabric, it should make the noise of a drum, indicating that there is sufficient tension. If there are still folds, sagging or bulging in the canvas, you’ll have to start again and maintain the tension throughout. Uneven tension in the fabric can cause cracking paint film issues later on.

20. If using a stretcher frame, it is possible to eliminate some of the looseness in the canvas by tapping the keys at each corner of the stretcher frame. But ideally, the canvas should be fairly tight from the get-go over a perfectly squared support frame.


Once your canvas has been stretched, it’s time to size, prime and tone your canvas before painting. Doing this the right way is vital, especially for oil painting on canvas. 


Using canvas pliers to stretch a canvas.


What is the difference between a stretcher and strainer frame for painting?

An artist’s canvas is usually attached to a support frame, called either a stretcher or a strainer.

The canvas is wrapped around the frame, and either nailed, tacked or stapled to the bars of the frame.

Stretcher/strainer frames are usually made from wood, such as obeche, pine, beech, basswood, poplar, or any kind of available hard or soft wood that is lightweight and durable.

Although not very common, sometimes they can be made from metal or plastic too. See also: Modernized Stretcher for Paintings on Canvas: Assessment and Observation by the American Institute of Conservation of Historic Artworks.

The wooden bars of a canvas stretcher frame (or French stretcher) have mitred joints cut at 45° at each corner. This allows the bars to slot into each other, and adds mobility to the frame, so that the outward tension on the canvas can be adjusted.

The bars of a strainer frame are fixed; the joints are glued and nailed or stapled together. Therefore, strainer frames lack the ability of being adjusted.

At each inside corner of the stretcher, two wooden ‘keys’ or wedges can be tapped into the slots of the mitred joints in order to increase the tension outwards.

If the canvas painting should sag over time, the wedges can be gently tapped deeper into the mitred slots with a small mallet or ball-peen hammer.

This forces the corners of the stretcher outwards and increases the canvas tension so that any sagging or bulging in the canvas is eliminated.


Commercially made stretcher (front) and strainer (back), made from obeche. Stretcher showing wooden keys. 


Strainer vs Stretcher Frame

Strainer Pros: Strainer Cons: Stretcher Pros: Stretcher Cons:
Easy to manufacture, design can be very simple. The bars can be joined together with a simple butt, dowel, or lap joint construction. If canvas begins to sag over time, the nails, staples or tacks will need to come out and the canvas re-stretched over the frame. This is time consuming and the canvas can be damaged in the process. Stretcher frames have adjustable corners with wooden keys that can be tapped, thus pushing the bars of the stretcher outwards, taking up any slack in the canvas. Difficult to construct quality stretchers. Mitred joints are more complicated and time-consuming to make.
Because strainers can easily be made by a competent artist or handyman, the quality and straightness of the wood can be closely examined. Exact custom sizes can be built quite easily. Since strainers can be easily built by hand (no complicated mitred adjustable corners that need specialised machining or craftmanship),  budget-built, DIY strainers are often heavy and bulky. Stretcher bars are usually machined as a single milled piece of wood with a beveled profile. Therefore lightweight. Commercially available stretcher frames can be very poorly constructed from inferior wood, and not to the specific dimensions you need.
Can be a very strong, rigid construction (especially if made with laminated bars, separate beveled lip and cross members), since corners are fixed and resist movement. Budget-built DIY strainers often lack beveled edges, so the canvas lies flat against the wooden strainer bar. This causes cracks, creases and ‘stretcher marks’. The beveled profile of the wooden stretcher bars prevents the canvas from lying flat against the wood and causing creases and cracks in the paint film. Excessive ‘keying out’ by over-adjusting the stretcher can cause tearing of the canvas, bowing or warping of the wood because of the strain, and cracks to form in the painting.
A rigid panel can be glued to a strainer frame to create a rigid support for the canvas to stretch over. This is the ideal support for painting on canvas as it induces the least amount of stress on the paint film. A rigid canvas support (panel glued to a strainer frame) can start becoming very heavy as the artwork increases in size. If the canvas painting is glued to a panel, it can be very difficult to remove without causing damage to the painting. With a well-constructed stretcher frame (including crossmembers), the artwork remains relatively light even with quite large paintings.  Tapping of keys can accidentally damage the painting.


A selection of stretchers and strainers for painting on canvas. Some strainers can be quite large.


How to make a strainer frame for stretching canvas

1. Select your pieces of wood for the bars of the strainer. Standard sizes of PAR (planed all round) wood may vary according to country, but generally I’ll use 22 mm x 44 mm pine or meranti. You can use whatever decent hard or softwood is available and choose the thickness according to the size of the painting.

2. Careful examination of the wood is vital. It must be straight and warp-free. Check for any bowing, cracks or knots in the wood. Put the length of wood flush against a straight wall or floor, rotating it onto every side, and check for any bends. It must be flat.

3. If you have a router or spindle moulder, the wood can be given a beveled profile so that the canvas will only be in contact with the outer edge of the strainer bar, and not lie flat against the wood, which will damage the painting. It’s best to router the total length(s) of wood before cutting them into shorter pieces.

4. If you do not have a router or spindle moulder to cut the profile, you can create a composite strainer bar by gluing quarter round moulding along the outer edge of the bar. Alternatively, you can glue a lattice strip/wooden cover strip along the outside edge to create a lip. This also serves to strengthen the strainer bar. (Or, if your picture is small enough, just make your strainer from quarter round moulding.)

5. Before cutting the bars to the required length for the strainer frame, it’s important to consider the kind of joint you’ll be using to join the corners of the strainer. Unlike a stretcher frame, the joints of a strainer do not use a movable mortise and tenon mitre joint. You can use a simple butt joint, or lap, dowel, or bridle joints, or simply use a framing guillotine and underpinner.

6. Cut the wood carefully to the required lengths, either by hand, or with a dropsaw, tablesaw, or use a framing guillotine. Depending on the joint you’ll be using, the cut will either be at 90° or 45°. 

7. Put the two long pieces of wood together side to side, and the same for the two shorter pieces (assuming the picture will be a rectangle. Otherwise, if square, all sides will be the same length). The corresponding lengths of the bars should be exactly equal.

8. Having cut the wood to size, you can then cut the required joints to join the bars of the strainer. Check the lengths against each other again to make sure they are exactly the same. Glue the joints together. If using an underpinner machine, glue the mitred ends before pinning.

9. Check ‘squaring-up’ while the glue is still wet, by measuring diagonally across the strainer corner to corner with tape measure. Both measurements across the diagonals should be equal.

10. If making a strainer frame for a large canvas, the joints of the bars can be glued together and then placed in a jig to square up before using the underpinner or being screwed together. This ensures that the strainer is perfectly squared beforehand. Alternatively, weights can be placed on the bars, or a picture framing clamp strap can be used while the glue sets.

11. Depending on the size of your strainer frame and the strength and thickness of the wood used, a single, double or even multi crossmember(s) may be necessary for added strength, and to prevent warping and bowing under the tension of the canvas.

12. When making your own strainer frame, you may decide to make a ‘box canvas’ instead of the normal ‘flat’ format. This means simply turning your wood sideways so that the width of the strainer bar determines the ‘depth’ of the canvas. The bars of the strainer are then cut and can be joined with mitred, dovetail or box joints.


Using a framing guillotine to cut the strainer bars.


Using an underpinner to make a strainer frame for a small canvas painting.


Painting on a rigid support

The best support for oil on canvas painting I’ve found, is actually a rigid support.

This may be a little heavier, but it gives the best protection for the painting. Canvas is prone to shinking and stretching with fluctuations in temperature and humidity, and over time, the paint film cracks, delaminates, or flakes off because of this movement.

The rigid support is also nice to paint on, as your hand doesn’t cause bouncing and ‘bowing in’ of the canvas, like when painting on a traditional flexible canvas support. 

A rigid support is easy to make, with a panel board glued to a stretcher/strainer frame, and then wrapped over with canvas, just like a normal stretcher/strainer.

For more info about painting on a rigid support, check out another one of my in-depth blogs: Making Your Own Canvas Panels for Oil Painting.



I hope you enjoyed these tips for how to stretch a canvas. A strainer frame is pretty easy to make compared to a stretcher, especially if you use a mitre saw or framing guillotine. 

If you want to know how to properly size and prime a canvas for oil painting, check out this extensive blog I wrote, Painting the Traditional Way – Part 1.


Thanks for reading, and please send me any comments, questions or suggestions in the comments section below. Tell me your tricks for making canvases, I’d really like to know.


You can also check out some of my figure paintings here.


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2 thoughts on “How to Stretch a Canvas for Painting — the Easy Way!”

  1. Hi! I am an art beginner. I am learning how to draw, and learning to work with watercolors. Recently I was given a small acrylic painting by a relative. Thus caused me to buy an inexpensive linen canvas so that I can test different varnishes on it and decide which varnish to use on the relative’s painting. I painted acrylic on the linen canvas. Nothing fancy, I just want to test the varnish, but it also gives me my first experience with linen and with stretched canvas. Then I noticed the linen sags a bit and needs to be stretched more. When I searched on my browser to learn how to use stretching keys, this article came up. It didn’t directly answer my question, but I did read your article and watch the video, and I quickly read another of your articles, too. Thank you for this content! I’m so new to art and really appreciate your showing how it is done. I learned many lessons from buying and painting the linen canvas and I’m learning from you, too. ….Bob

    1. Thank you Bob. I appreciate your lengthy reply. Sorry if you already received this message. I had issues with my comments section. Some of the cheaper art store canvases have keys. But the keys are more for show and totally useless when the bars of the stretcher have been stapled together, thus defeating the whole purpose of being able to push the bars further out by knocking in the keys. It should be easy to reduce the sag in the canvas. Also don’t scrub the hell out of the canvas when painting with a brush. A canvas glued to a rigid panel is going to be your best bet. It’ll last much longer than a canvas (i.e. Flemish paintings on wooden panels dating from 1400’s). But canvas is convenient when working very large.

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