Canvas Frame and Stretcher Bar Buying

Canvas framing is arithmetic before it is a product. A frame has an inner size and an outer size, a stretcher bar has a length, a width and a depth, and a canvas has to clear the rebate and sit on a frame that will not twist. This guide sets out how a framer or art-supply buyer orders the two, and where the market's listings most often mislead.

The measures

Measure	Definition	Typical trade range	Why it matters
Inner size	the canvas opening	standard frame sizes	matches the canvas the customer has
Outer size	inner size plus twice the bar width	inner plus about 4-8 cm	shelf fit and the customer's frame rebate
Bar width	face width of the moulding	approx. 20-40 mm	visual weight, and the outer size
Bar depth	how far the frame stands off the wall	approx. 20-40 mm	clears the stretcher and the hardware
Units per carton	how many ship together	stated per model	the landed cost on a volume order

Inner size is the number a framer buys by. The most common listing error is to publish an outer size and call it the frame size, which leads a buyer to order a frame that is one bar width too large for the canvas.

Frames or bars

A canvas frame is a pre-cut, assembled frame in a standard size, ready to take a stretched canvas or a print. It is bought by inner size and sold as a finished item.

Stretcher bars are four lengths a framer assembles to whatever size the order needs, with a rebate at the face and a joint at each corner so the canvas can be tensioned with wedges.

Most framers stock both. The frames cover the common retail sizes and the bars cover the bespoke work. A range that stocks only frames turns away the customer who brings in an odd size; a range that stocks only bars makes the standard sizes slower to sell.

The bar section decision

The depth of the bar is the number that decides whether the stretcher clears the frame rebate, and it is the number most often missing from a listing.

Section	Typical use	What to confirm
about 20 mm	light cotton canvas, standard frames	clears a standard rebate
about 25-30 mm	general canvas work, gallery wrap	depth under the moulding
about 35-40 mm	heavy canvas, large formats	canvas weight and corner strength
bar length	matched to the frame size ordered	length tolerance, pre-notched or not

Two depths cover most framers' work: a shallow bar of about 20 mm and a deeper bar of about 35-40 mm. The width is a visual and weight decision; the depth is the fit decision.

Cartons and the order shape

Bars and frames are flat, long and light, so the order is a freight decision before it is a product decision:

Bars ship in long cartons, and a carton that is 20 cm longer changes the freight per unit more than a small difference in unit cost.
Frames ship flat in multiples, and the units per carton is the figure to compare between models.
Wedges and keys are a separate small part. A tensioning frame without wedges is incomplete for a framer, and the wedge is the cheapest thing to put in writing with the first order.
Long formats over about 90 cm need a cross-brace or a centre-bar, so confirm whether the bars are pre-notched.

The decision rule

Order by inner size, confirm the bar depth against the frame rebate, and compare models on units per carton rather than on the unit alone. Then write the wedge and the notching into the first order: a frame range that arrives complete sells as a range, and one that arrives missing the small parts turns every second order into a support conversation.