Mortise and Tenon Joint: Cut and Fit It in 5 Steps

A mortise and tenon joint joins a projecting tongue on one piece of wood to a matching pocket in another. For a clean furniture joint, cut the mortise first, fit the tenon to it, and make the shoulders close without using a clamp to force them home.

This guide takes you through one stopped, square-shouldered rail-to-leg practice joint. The key is not a magic fraction: it is keeping every layout and fit check tied to the same reference face. A tight-looking shoulder can hide a badly fitting tenon, so check both.

The workshop photographs are AI-generated editorial images, not measured examples or CarpDraw output. Use the dimensioned diagram and your own test pieces for layout. The wood shown varies between images; this is not a comparison of wood species or a photo record of one build.

A tabletop needs a different glue and movement plan: see how to fit pinned breadboard ends before applying a rail-to-leg method to a cross-grain end rail.

Size one practice joint before cutting

Start with flat, square stock of known finished thickness. For this exercise, use a rail 3/4 in (1.905 cm) thick and 2 in (5.08 cm) wide. The receiving leg is 1 1/2 in (3.81 cm) square. Make this on spare stock before cutting a furniture part.

Every measurement below is illustrative, not an industry standard or a structural recommendation. Inch dimensions control this example; metric equivalents are rounded where necessary. A chair, bed or heavily loaded table needs a joint designed for its loads, timber and surrounding construction.

Part or feature	Illustrative inches	Illustrative centimeters	What to check
Finished rail thickness	3/4 in	1.905 cm	Measure after planing
Finished rail width	2 in	5.08 cm	This is the vertical width in the drawing
Receiving leg section	1 1/2 x 1 1/2 in	3.81 x 3.81 cm	Straight grain around the pocket
Tenon thickness	1/4 in	0.635 cm	Fit to the actual mortise
Tenon width	1 1/2 in	3.81 cm	Leaves an equal top and bottom shoulder
Tenon length	1 in	2.54 cm	Measured from the shoulder
Mortise opening	1/4 x 1 1/2 in	0.635 x 3.81 cm	Same nominal section as the tenon
Mortise depth	1 1/16 in	2.699 cm	Check with a depth stick
Bottom clearance	1/16 in	0.159 cm	Depth minus tenon length
Each rail shoulder	1/4 in	0.635 cm	Face and edge shoulders in this example

The familiar one-third rule gives a starting tenon thickness, not a finished fit tolerance. Here, 3/4 divided by three is 1/4 in. Across the rail face, a 1 1/2 in tenon inside a 2 in rail leaves 1/4 in at the top and bottom. Across its thickness, the centered 1/4 in tenon leaves 1/4 in on each side.

Center the mortise across the leg face for this exercise. That leaves 5/8 in (1.588 cm) of wood on each side of its opening. A 1 1/16 in deep pocket in the 1 1/2 in leg leaves 7/16 in (1.111 cm) behind it. Those arithmetic checks help catch a layout mistake; they do not prove strength.

Keep the mortise away from the leg end and from any other joint. In a real table corner, a second rail can enter the adjacent face and meet the first tenon inside the leg. Draw that intersection before borrowing these example sizes. For a broader choice of construction, see the guide to wood joints in furniture.

When a rail forms a table base, agree the apron depth and chair clearance before sizing its joints, so the frame and the seated user both fit the design.

Mark the reference faces and shoulder lines

Choose one broad rail face and one adjacent edge as references. Mark them with a pencil face mark. Do the same on the leg, and keep track of which surface faces the outside of the furniture. A square checks squareness only against the surface it touches; swapping to a twisted or uneven face changes the result.

Gather a marking knife, sharp pencil, square, marking gauge, suitable mortise chisel, mallet, fine saw and clamps. A sharp paring chisel helps with the final fit. Secure the work before cutting and keep your free hand behind the cutting edge. Use the protection and safe workholding required by your tools.

Knife the shoulder line around all four rail faces at the intended tenon length. Carry the line around with the square registered against your marked reference surfaces. If the last line does not meet the first, stop and check the stock before making a saw cut.

Set the mortise gauge to the actual chisel or cutter width. Transfer that setting to the mortise and tenon without resetting it by eye. Mark waste clearly. A thick pencil line is not a fit allowance: saw on the waste side, leave the line and pare to it later.

Measure the rail's finished shoulder-to-shoulder length separately from its blank length. If the rail has a 1 in (2.54 cm) tenon at each end, the blank needs 2 in (5.08 cm) beyond the finished distance between shoulders. Forgetting that allowance creates a short rail that careful fitting cannot fix.

For a narrow table project, establish the overall console table dimensions before locating rails. Rail position affects how much leg remains around the mortise, not just the appearance of the finished table.

Cut the mortise first, then fit the tenon

I would cut the mortise first for a hand-tool practice joint. Its width is governed by the chisel and the way you cut; the exposed tenon cheeks are easier to trim to that actual opening. Make a complete trial joint before laying out a set of rails.

Do not use glue as a lubricant to rescue an untested fit. Water-based glue can make a tight joint harder to assemble, and the clock starts as soon as you spread it. Have the dry assembly, clamps and cleanup ready first.

For this example, the tenon ends short of the mortise bottom. That gap is intentional. The shoulders should land against the leg while the tenon still has room at its tip. A bottomed-out tenon can leave an open shoulder even when both parts look correctly cut.

Dry-fit, fix mistakes and write down the result

A good dry fit closes the shoulders, holds the rail square and comes apart for glue without torn fibers. The tenon should not rattle in the pocket. It also should not need heavy blows or extreme clamp pressure. Inspect both cheeks, all shoulders and the angle; no single check replaces the others.

Symptom	Likely cause to check	Next action
Shoulder stays open on every side	Tenon too long or chips at the bottom	Measure depth and clear the pocket
One shoulder closes before the other	Unequal shoulder lines or angled cheeks	Check against the reference face
Tenon starts then jams	Tapered pocket or thick area on a cheek	Find the contact mark and pare locally
Joint rocks when seated	Loose cheeks or damaged pocket walls	Repair with fitted wood or remake the part
Leg splits during assembly	Forced fit or too little surrounding wood	Stop; do not hide the damage with glue

Avoid sanding every face until the tenon slips in. That rounds edges and can turn one tight area into a loose joint everywhere else. A sharp tool used on a visible high spot gives better control. If the fit is badly loose, remake the practice piece; more ordinary wood glue is not a substitute for well-fitted wood.

For glue-up, use an adhesive suited to your wood and service conditions. Spread a thin, even coat on the mating surfaces following the maker's instructions, assemble within its working time and clamp without distorting the frame. Check diagonals on a complete rectangular assembly and check square at each corner. Follow the glue label for clamp time and full cure before loading. Titebond's wood-glue guidance explains why fit, temperature and assembly time matter.

Turn the successful test into a workshop brief

Record the actual stock thickness, mortise location, pocket depth, tenon dimensions and reference faces. Add a section through the leg and a view showing the shoulders. Label the drawing with the date and say which dimensions were measured on the test piece. The furniture technical drawing guide explains how separate views reduce ambiguity.

A photo of the finished outside corner cannot show the buried tenon length or the remaining wood behind the pocket. That is the limit of a photo-only brief. Solve it manually with measured sections and a test joint, not an estimate from perspective. Keep the test piece until the maker has accepted the detail. If the same furniture also has a plywood cabinet back, specify its rabbet seat and panel fit separately from the frame joint.

Use CarpDraw as the project starting point, not as approval of these sample dimensions. The physical trial joint and the maker's review remain the checks that matter.

For a flat frame corner with a broad overlap, our half lap joint cutting guide shows how to keep both faces flush.

When the task is a coplanar panel seam rather than a loaded frame connection, the five-step biscuit panel guide explains how to keep board faces flush during glue-up.