When do I need cross braces?

A practical rule of thumb is to add a brace once a bar runs past roughly 85-90 cm (about 34-36 inches), and to use a full cross of horizontal and vertical braces on canvases over about 110 cm (44 inches). The threshold in this calculator defaults to a conservative 60 cm so it errs towards more support — raise it under Advanced Options if you are working at the larger trade thresholds. Cross braces stop the long bars from bowing inward under canvas tension.

How much wrap allowance should I add?

Leave 7-10 cm (3-4 inches) of fabric beyond the painting face on each side. That margin has to span the bar depth to reach the back of the frame, then leave roughly 2.5 cm (1 inch) of flap to staple down. This calculator builds the fabric size as canvas + (wrap allowance × 2) + (bar depth × 2), so deeper gallery bars automatically demand more cloth.

Mortise and tenon vs mitre joints?

Mortise and tenon (tongue and groove) joints are the strongest and accept corner keys (wedges) so you can re-tension the canvas later — bars are cut to the assembled outer size and slot together. Mitre joints look clean but each bar is cut to the full outer length with 45° ends and they cannot be keyed. Stapled butt joints are simplest but weakest and need a corner brace or angle plate. For lasting work, choose mortise and tenon.

What bar depth should I choose?

18 mm bars suit small works under about 40 cm. 38 mm is the standard gallery profile for most sizes. 50 mm (deep edge) gives a gallery-wrap look with more rigidity for larger pieces. A deeper bar resists warping and needs more wrap fabric (the calculator adds the depth to each side automatically).

Canvas Stretcher Calculator — Stretcher Bar Cutting

Calculate stretcher bar lengths, canvas fabric and materials for custom canvases.

Canvas Width

Finished painting width (outer frame size)

Canvas Height

Finished painting height (outer frame size)

Bar DepthStandard gallery profiles, or enter a custom bar depth

Corner TypeSets the assembly note and cutting method

Quantity

Number of identical canvases to build

How We Calculate This

Stretcher Bar Calculations

Bar lengths: 2 bars at the canvas width + 2 bars at the canvas height. Bars are cut to the assembled outer dimension regardless of joint type.

Canvas fabric = canvas size + (wrap allowance × 2) + (bar depth × 2). The cloth spans each bar's depth to reach the back, then leaves a stapling flap.

Cross braces: Added when a dimension exceeds the threshold (default 60 cm — conservative; trade thresholds are nearer 85 cm). A brace runs across the dimension that triggered it.

Staples: A single row along the back face, roughly one every 6 cm, plus a couple per corner for the folds. There is no front row — the front is the painting surface.

Weight is an informational estimate from kiln-dried pine gallery bars (~280 g/m at 38 mm) and 10 oz cotton duck (~340 g/m²); it varies with bar species, profile and canvas grade.

Frequently Asked Questions

Last updated: March 2026

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