When do I need a cross brace?

Suppliers disagree on the exact trigger: Fitzroy Stretches recommends a single brace once a side reaches 44 in (about 1100mm), UCS Art suggests bracing bars over 34 in, and gallery-wrap (deep-edge) bars often bow noticeably by 40 in. This calculator defaults to a conservative 900mm (about 35 in) so smaller canvases are still supported, but you can raise the threshold under Advanced Options if you are using deeper, stiffer bars. Beyond 1500mm a second brace stops the long bars bending inward under canvas tension.

What are corner keys?

Corner keys (also called canvas wedges) are small wooden or plastic wedges tapped into slots at each mitred corner. Driving them in spreads the bars apart very slightly, re-tensioning a slack canvas. The standard convention is 2 keys per corner, so a plain four-bar canvas takes 8 keys; each cross-brace junction adds another 2.

What wood are stretcher bars made from?

Most commercial stretcher bars are kiln-dried pine or fir with a raised front lip that holds the canvas off the flat back of the bar (so the edge does not print through the painting). Premium bars use poplar or basswood for lighter weight and less warping. Always measure and order by the outer (finished) dimensions of the canvas.

ArtCalcs

Stretcher Bar Calculator

Work out stretcher bar lengths, cross braces and corner keys needed for your canvas.

Canvas Width

Outer width of the finished canvas — stretcher bars are sold and labelled by this dimension

Canvas Height

Outer height of the finished canvas — measure the front face, not the wrapped edge

How We Calculate This

Every stretched canvas needs 4 bars (2 for the width, 2 for the height). Cross braces add rigidity once the bars get long enough to bow inward under canvas tension. Thresholds below use the longest side and can be adjusted in Advanced Options.

900mm and under longest side: no cross brace
Over 900mm up to 1500mm: 1 cross brace
Over 1500mm: 2 cross braces

Keys = (4 corners + 2 per cross-brace junction) × keys per corner, e.g. a plain canvas at 2 keys per corner = 8 keys. Brace trigger follows Fitzroy/UCS supplier guidance (44 in / 34 in respectively); 900mm is a deliberately conservative default.

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates. Always verify quantities before purchasing materials.