Want to Stretch a Canvas? What You Need to Know

Although it is much easier to buy an already stretched canvas, some artists still prepare their own canvas for their work. For example, those who need specific dimensions, whose painting technique is not suited to a universal primer, or who cannot find the canvas thickness and texture they are looking for. Another reason to buy stretcher bars and canvas by the roll separately is transportation. Some artists travel often and need their painting materials to be transported without damage.

Once you decide what size your painting should be, the first step in stretching canvas is to buy wooden stretcher bars. Although it may seem simple, you need to plan carefully how many bars you need, because the stability of the frame depends on it. An unstable frame risks warping when the canvas is stretched, and the painting on the canvas will not look good.

The Challenge of Choosing the Right Stretcher Bars

Once you know the dimensions, it is time to choose the right stretcher bars. Do not underestimate the planning. The stability of the entire frame depends directly on choosing the right number and type of bars. An insufficiently stable frame risks warping when the canvas is stretched, and the painting will not look good.

Wooden stretcher bars fall into two categories: side bars and crossbars. It is important to know that crossbars (gallery bars) have teeth that fit into the main stretcher bars they are inserted into.

Frames Up to 70 cm Long

For a frame up to 70 cm long, 4 side bars are enough. If the frame measures, for example, 70x50 cm, you need two 70 cm bars and two 50 cm bars. In this case, a crossbar is not needed. However, you can add one to reinforce the frame if you wish. To calculate its length, subtract the width of the bars on both sides from the length of the shorter side of the frame.

If the side bars you are using are 3.5 cm wide, you need a crossbar that is 7 cm shorter than the shorter side of the frame. So, if you have a 50x70 cm frame, the crossbar should be 43 cm long so it sits exactly in the center of the longer bar.

Frames Over 70 cm Long

If one or both sides of the frame are longer than 70 cm, you also need center bars to reinforce it. All gallery stretcher bars longer than 70 cm have an inside notch for inserting a center bar, and all center bars longer than 70 cm have a tooth that catches on the side bar when inserted.

For example, if you want a 60x90 cm frame with gallery stretcher bars that are 4.5 cm wide.

You need:
- 2 side bars, 60 cm long
- 2 side bars, 90 cm long
- 1 center bar, 51.2 cm long [60 cm - 9 cm = 51 cm], placed on the 90 cm bars

Frames Over 100 cm Long

If both frame dimensions exceed 100 cm, reinforce it with bars that cross to form an X. As in the previous example, calculate the lengths of the center bars, but this time you’ll need two bars.

For example, for a 100 x 130 cm frame with 4.5 cm-wide side bars, you need:
- 2 side bars, 100 cm long
- 2 side bars, 130 cm long
- 1 center bar, 91.2 cm long [100 cm - 9 cm]
- 1 center bar, 121.2 cm long [130 cm - 9 cm]

Frames in Elongated Formats

You may be wondering what type of center bars you need in these cases, and assembling a frame like this is quite complicated. We recommend using standard center bars.

For example, to make a 150 x 50 cm frame with 4.5 cm-wide bars, you need:
- 2 side bars, 150 cm long
- 2 side bars, 50 cm long
- 2 center bars, 41.2 cm long, placed at equal distances

These bars are 2 mm longer because they don’t have a tooth to fit into the notches in the side bars. You can place them anywhere along the side bars, but we recommend spacing them evenly. Depending on the length of the side bars, you can use one, two, or three center bars.

Corner Problems

Assembling the corners is intuitive, but make sure the bars are level with one another. Use a square to check that all the corners are truly right angles. You can tap gently with a hammer to join them more securely.

Positioning the Center Bar

Positioning center bars with a tooth is easy, since you simply insert them into the existing notches in the side bars. When crossing bars, you’ll also see that you need to overlap them and tap gently with a hammer to secure them.

Positioning standard center bars without teeth or notches may seem complicated, but all that matters is that they are centered or spaced symmetrically and positioned at a right angle. Place them between the main bars and fasten them with nails or a staple gun. We always recommend reading the product description and checking the bar thickness, since you can combine side and center bars only if they are from the same series, meaning they have the same width.

As you’ve already noticed, we offer bars in different widths: 4.5 cm and 3.5 cm. Always check the bar thickness in the product description. You can combine only bars from the same series that have the same width.

Gallery stretcher bars that are 4.5 cm wide can be crossed and have notches and teeth that make joining them easier. You can build frames up to 150x200 cm.

Standard PROFI stretcher bars with a width of 3.5 cm cannot be cross-braced and have no cutouts, but their ends are completely straight. Simply place them inside the frame (between the side bars) and secure them with staples or nails. The longest center bar is 93.2 cm, which means the largest possible frame is 200x100 cm.

In the next article, we’ll look at how to handle 4 other common challenges when stretching a canvas.