How do I set out architrave with an even reveal?

The reveal is the small setback of the architrave from the frame edge, and marking it consistently before any cut is what makes the mitres close and the door look right.

Difficulty: intermediate
Time: 1 hr
Read: 5 min

Short answer

Mark a consistent reveal — a small setback, commonly a few millimetres — along both legs and the head of the frame with a gauge or a marking block, before cutting anything. Cut and fit the head first to the marked lines, then the legs up to it. Mitres only close if both pieces are set out from the same reveal line.

Architrave that looks wrong almost always has an inconsistent reveal: wider at the top than the bottom, or different on the two legs. The eye reads the parallel line between frame and architrave far more readily than it reads the architrave itself, so setting that line out accurately is most of the job.

What you'll need

a marking gauge, a combination square, or a small offcut used as a block
a mitre saw or a mitre box
pins or a nail gun, and wood glue
a sharp pencil
a block plane or sanding block (optional)

Step by step

Check the frame is square and plumb first.Architrave cannot fix a frame that leans. Measure the diagonals of the opening and check the legs with a level; a frame out of square means the mitres will need adjusting from 45 degrees.
Choose the reveal and stick to it.A small consistent setback from the inner edge of the frame — enough to show a deliberate line and to give the hinges and the door stop room. Whatever you choose, it must be identical everywhere.
Mark the reveal with a gauge or a block, not a tape.Set a combination square or use a small offcut of the right width as a marking block, and run it along the frame with a pencil against it. This is what makes the line consistent; measuring each mark separately is what makes it wander.
Mark both legs and the head before cutting anything.All three lines drawn first means you are cutting to a set-out rather than making it up as you go.
Cut and fit the head first.Mitre both ends of the head piece, measuring the long points from the intersections of the reveal lines rather than from the frame itself.
Pin the head lightly so it can still be adjusted.A couple of pins holds it while the legs are offered up. If the mitres need easing, you have not committed.
Cut the legs long and creep up on the fit.Mitre the top of each leg, offer it up, and trim the bottom to length. Cutting long first means a trial fit can be corrected; cutting to the measured length means an error is final.
Adjust the mitre angle if the frame is out of square.A frame whose corners are not 90 degrees needs mitres that are not 45. Small adjustments on the saw, tested with offcuts, close the joint.
Glue and pin the mitres.Glue on the mitred faces and pins driven through the joint from the edge lock it. A mitre relying on being pushed together opens as the timber moves.
Scribe the bottom of the legs to the floor if it is uneven.Better than leaving a gap and caulking it, particularly on a hard floor where the gap is visible in raking light.

Tips

Make a small hardwood marking block cut to your chosen reveal. It marks all three sides identically in seconds and it can be reused on every door in the house.
Fit all the architrave in a house to the same reveal, or the difference between rooms will nag at you.
Where the floor is carpeted and the architrave stops short, decide the bottom detail before cutting — a plinth block is an option that avoids scribing entirely.
A slight back-bevel on the mitre helps the front edges close tight, the same principle as easing a skirting mitre from behind.

Common mistakes

Cutting the architrave to the frame edge with no reveal — It makes any inaccuracy in the frame or the architrave brutally obvious, because there is no visual break between the two. The reveal is a deliberate shadow line that lets small discrepancies disappear.
Measuring the reveal with a tape at each point — A tape read to the nearest millimetre by eye, several times, produces a line that wanders visibly. A gauge or a block gives exactly the same setback every time without any reading at all.
Cutting the legs to a measured length before trial fitting — Any error in the mitre angle or the head's position changes the required length, and a leg cut short cannot be recovered. Cut long, offer up, trim.

If it doesn't work

Mitre open at the outer edge

Cause: Frame corner is more than 90 degrees, or the mitres were both cut at exactly 45 — Fix: Adjust the saw a degree at a time, testing with offcuts, until the joint closes.

Reveal wider at the top than the bottom

Cause: Marked by measurement rather than from a gauge, or the frame is not parallel — Fix: Re-mark with a block. If the frame itself is out, split the difference so the discrepancy is shared rather than concentrated.

Mitre opened a few months after fitting

Cause: Not glued and pinned across the joint — Fix: Work glue into the joint, pull it closed and pin through from the edge, then fill and touch up.

Questions people ask

How big should the reveal be?

Small and consistent is what matters more than the exact figure — a few millimetres is the usual domestic look, and matching whatever exists elsewhere in the house is usually the right call. On a door with hinges, the reveal must at least clear the hinge knuckle.

Do I have to mitre, or can I use plinth and corner blocks?

Blocks are a legitimate traditional alternative: square-cut architrave running into a decorative corner block at the top and a plinth block at the bottom. They avoid mitres entirely, which suits a frame that is badly out of square, and they suit period styles.

How do I deal with architrave meeting skirting?

The architrave normally runs down past the skirting, and the skirting is cut to butt into it — which is why architrave usually goes on first, or at least is planned first. A plinth block, being thicker than both, resolves the junction neatly where the skirting is deep.