Picture frame moulding explained

Moulding is the frame. Everything else in the assembly — glazing, mat, backing — is bought by size, but the moulding is bought by the foot, chosen by profile, and is what determines whether the finished object looks like furniture or like packaging.

Reading a moulding specification

A supplier's listing gives four numbers, and each one decides something.

Face width is how wide the frame looks from the front. This is the primary design number.

Height or depth is how far the moulding stands off the wall.

Rabbet depth is how much room there is inside for contents. This is the number that determines whether your frame will actually close.

Rabbet width is how far the moulding overlaps the contents — usually a quarter to three eighths of an inch. This is why glazing and mats are cut a fraction under the nominal size.

A typical listing might read: face 1.5", height 0.875", rabbet 0.5" x 0.375". That describes a frame an inch and a half wide on the face, standing seven eighths of an inch proud, able to hold half an inch of contents, overlapping them by three eighths.

Rabbet depth is the constraint nobody checks

Add up what has to fit inside:

A single-matted print therefore needs about 0.26 inches; a double-matted one about 0.32; and a stretched canvas needs three quarters of an inch or more on its own. A quarter-inch rabbet, which is common on decorative mouldings, will not close over a double mat.

When a rabbet is too shallow there are two honest fixes: deepen it with a router or a table saw before assembly, or use a frame extender strip glued to the back. Forcing the backing in and hoping is not a fix; it bows the artwork against the glazing.

Profiles and what they do

The cross-section of the face is not decoration alone. It directs the eye.

Flat. A plain rectangular face. Neutral, modern, and the most forgiving profile for contemporary work. Reads as a border rather than a frame.

Scoop. Concave, sloping down toward the artwork. The classic gallery profile — it physically funnels attention inward and gives depth without ornament.

Cove. Concave sloping the other way, rising toward the outer edge. Creates a sense of a window looking through.

Ogee. An S-curve. The traditional profile of period framing, and the base shape underneath most ornate gilt work.

Cushion. Convex, bulging outward. Soft and rounded; suits oil paintings and reads as older.

Reverse. Highest at the inner edge, sloping away outward. Unusual, quite assertive, and effective at making a small artwork feel more important.

As a rule, the profile should oppose the artwork's character rather than echo it. A busy ornate frame around a busy image is exhausting; a flat frame around a densely detailed etching gives it somewhere to breathe.

How much to buy

The arithmetic is straightforward and people still get it wrong, because a mitre consumes material at both ends of every rail.

For a frame of width W and height H, in moulding of face width F:

Total length = 2(W + H) + 8F + waste

The 8F term is the four corners, each of which needs F extra on both meeting rails.

Worked example, an 11x14 frame in 2-inch moulding:

• Sides: 2 × (11 + 14) = 50 inches
• Corners: 8 × 2 = 16 inches
• Subtotal: 66 inches
• Waste allowance (10%): 7 inches
• Buy 73 inches — call it 6 feet 6.

For a 24x36 frame in 2-inch moulding: 120 + 16 = 136 inches plus waste, so 12 feet 6. Note that suppliers sell in fixed stick lengths, usually 8 or 9 feet, so a 24x36 frame needs two sticks and leaves a substantial offcut. That offcut is exactly why frame shops accumulate a scrap bin, and why asking for offcuts is sometimes worth doing.

Length, chop and join

Suppliers sell the same moulding three ways, and the price differences are instructive.

Length. Full sticks, cheapest per foot, you cut everything. This is the right choice if you have a mitre saw you trust and are making several frames.

Chop. The supplier cuts your four pieces to exact size with the mitres already made. You glue and join them. Costs perhaps 30 to 50% more than length, and removes the single hardest step. For one frame in an expensive moulding, chop is usually the smart purchase — a botched mitre in walnut costs more than the chop fee.

Join. Arrives assembled and ready to fill. Most expensive, and worth it for large frames where clamping is genuinely difficult.

Where to buy

Framing wholesalers carry hundreds of profiles and will often sell to the public, either by the stick or as a chop. This is where the real range is.

Independent frame shops will sometimes sell length or chop from their own stock, and some will sell offcuts cheaply. Worth asking.

Online moulding suppliers ship by the stick with an oversize-freight charge that makes small orders uneconomic and large ones fine.

Home improvement stores sell architectural trim, not frame moulding. It has no rabbet. You can make a frame from it by cutting a rabbet yourself on a table saw, and people do, but you are adding a machining operation and the proportions of door casing rarely suit a picture.

Choosing a width

The moulding should sit in proportion to the artwork and, if there is one, to the mat.

And one relationship that matters more than the absolute number: if there is a mat, the mat border should be wider than the moulding face. When the moulding is wider, the frame reads as the subject and the artwork as an inset. That is occasionally the intention — heavy ornate framing of small oils does it deliberately — but it is almost never what someone framing a photograph wants.

Once you have the moulding, the step-by-step build guide covers cutting, joining and finishing it. If you are choosing the timber rather than a ready-made profile, start with the best wood for picture frames.