Free mortise and tenon calculator for traditional joinery. Calculate joint dimensions, mortise depth, tenon thickness, and fit tolerances. Includes strength guidelines and sizing charts for furniture and timber framing. Create perfect-fitting joints every time!
Enter your stock dimensions and joint specifications, then click "Calculate Joint Dimensions" to see your mortise and tenon measurements.
Traditional mortise and tenon proportions follow the "rule of thirds" for optimal strength. Note: These are general guidelines based on traditional woodworking practices. Adjust based on specific wood species, application, and structural requirements.
Mortise Width = Stock Thickness ÷ 3 | Application | Tenon Length | Stock Thickness | Typical Projects |
|---|---|---|---|
| Light-Duty | 1"-1.5" | 3/4"-1" | Picture frames, small boxes |
| Standard Furniture | 2"-2.5" | 1.5"-2" | Chair rails, table aprons |
| Heavy-Duty | 3"-4" | 2"-3" | Bed frames, workbenches |
| Structural | 4"+ | 3"+ | Timber framing, beams |
Proper fit tolerances ensure strong joints without splitting. Note: Actual tolerances depend on wood species, moisture content, cutting precision, and assembly conditions.
| Wood Type | Species | Tolerance | Characteristics |
|---|---|---|---|
| Hardwood | Oak, Maple, Cherry, Ash | 0.005"-0.010" | Dense, stable, excellent strength |
| Softwood | Pine, Fir, Cedar, Spruce | 0.008"-0.015" | Softer, more prone to compression |
| Exotic | Teak, Mahogany, Walnut | 0.005"-0.012" | Variable density, oil content |
| Engineered | Plywood, MDF | 0.010"-0.020" | Dimensionally stable, less glue adhesion |
| Tool | Best For | Advantages | Skill Level |
|---|---|---|---|
| Hand Tools (Chisels, Saws) | 1-5 joints, custom work | Quiet, precise control, traditional | Intermediate+ |
| Drill Press + Chisels | 5-20 joints, mixed sizes | Faster waste removal, accurate depth | Beginner+ |
| Router Table | 10+ identical tenons | Consistent results, efficient | Intermediate |
| Mortising Machine | Production, 20+ joints | Fast, square mortises, repeatable | Beginner+ |
| Table Saw + Jig | Tenons, production work | Accurate, repeatable cuts | Intermediate |
Always cut the mortise first, then fit the tenon to match. Mortises are harder to adjust than tenons. Use the mortise as your reference and carefully pare the tenon for a perfect fit. This approach reduces errors and ensures tight-fitting joints.
Apply glue to mortise walls, not the tenon. This prevents glue from being scraped off during assembly and ensures even distribution. Use a small brush or glue syringe to coat all four mortise walls.
A rectangular hole or slot cut into wood to receive a tenon. Can be blind (stopped), through (complete), or open (one end open). The mortise width should be 1/3 of the stock thickness.
A rectangular projection cut on the end of a board to fit into a mortise. Thickness matches mortise width. Length determines joint depth and strength.
A mortise that does not go completely through the workpiece. The joint is hidden from one side. Most common type for furniture construction.
A mortise cut completely through the workpiece. The tenon extends through and is visible from both sides. Often wedged for additional strength.
A tenon with a small step (haunch) cut into the shoulder. Prevents twisting and fills the groove in frame-and-panel construction. The haunch is typically 1/3 of the tenon width.
A through tenon that is split and wedged after insertion, expanding the tenon inside the mortise for a permanent mechanical lock. Extremely strong.
The traditional proportioning rule where mortise width equals 1/3 of stock thickness, leaving 1/3 material on each side. Provides optimal balance of joint strength and surrounding material integrity.
The clearance between mortise and tenon surfaces. Tight: 0.002"-0.005". Standard: 0.005"-0.010". Loose: 0.010"-0.015". Affects joint strength, assembly ease, and glue performance.
The traditional rule is that mortise width should be 1/3 of the stock thickness, and tenon thickness should match the mortise width. This provides optimal strength while maintaining sufficient material around the mortise to prevent splitting.
Typical clearances are approximately 0.010"-0.015" for hardwoods and 0.015"-0.020" for softwoods in humid climates. Consider wood species movement characteristics and final environment conditions. Quarter-sawn lumber generally moves less than plain-sawn.
Always cut the mortise first, then fit the tenon to match. Mortises are harder to adjust than tenons. Use the mortise as your reference and carefully pare the tenon for a perfect fit.
Essential tools include: sharp chisels (1/4", 3/8", 1/2"), mortise gauge, tenon saw or dovetail saw, drill bits for waste removal, and a mallet. Power tools like mortising machines and table saws can speed production.
Use sharp tools, score the mortise outline first, remove waste gradually, and support the work piece properly. Clamp a backing board to prevent tear-out. For deep mortises, drill out most waste before chiseling to final dimensions.
Blind mortises don't go completely through the stock, hiding the joint. Through mortises go all the way through and are often wedged for extra strength. Blind joints look cleaner but through joints can be stronger and easier to cut accurately.