Joinery sizing planner
Mortise and Tenon Size Calculator
Size furniture joinery from the actual rail, stile, and post dimensions, with shoulder layout, haunch allowance, glue clearance, drawbore offset, load adjustment, and glue surface area.
Pick a common furniture joint, then tune the dimensions to match the stock on your bench.
Joinery layout breakdown
| Rail thickness | Light frame tenon | Medium furniture tenon | Heavy or racking tenon | Layout note |
|---|---|---|---|---|
| 1/2 in | 5/32 to 3/16 in | 3/16 in | 3/16 to 1/4 in | Keep shoulders crisp; avoid a fragile thin cheek. |
| 3/4 in | 1/4 in | 1/4 to 5/16 in | 5/16 in | Common cabinet door, face frame, and small table size. |
| 1 in | 5/16 in | 3/8 in | 3/8 to 7/16 in | Good for aprons, bench parts, and wide rails. |
| 1-1/2 in | 1/2 in | 1/2 to 5/8 in | 5/8 in | Leave enough post wall behind deep mortises. |
| 2 in | 5/8 in | 3/4 in | 3/4 to 7/8 in | Use double tenons if a single tenon gets too wide. |
| Receiving member | Typical tenon length | Minimum back wall | Drawbore offset | Best use |
|---|---|---|---|---|
| 3/4 in stile | 3/8 to 1/2 in | 3/16 in | None or 1/64 in | Doors, face frames, and light casework. |
| 1 in stile | 1/2 to 5/8 in | 1/4 in | 1/64 to 1/32 in | Cabinet rails and small frames. |
| 1-1/2 in post | 3/4 to 1 in | 3/8 in | 1/32 in | Tables, benches, and medium posts. |
| 2 in post | 1 to 1-1/4 in | 1/2 in | 1/32 to 3/64 in | Bed rails, workbench bases, and heavy stretchers. |
| 3 in post | 1-1/2 to 2 in | 5/8 in | 3/64 in | Large trestles and knockdown bed hardware blocks. |
| Haunch option | Width allowance | Use with | Shoulder effect | Cutting note |
|---|---|---|---|---|
| No haunch | 0 | Aprons and stretchers | Full long tenon width | Simplest layout when no groove must be hidden. |
| One-third rail width | About 33% | Cabinet and door rails | Long tenon becomes shorter | Hides a panel groove and resists twist at the end. |
| One-quarter rail width | About 25% | Narrow rails | More glue area than a larger haunch | Useful when the rail is too narrow for a large haunch. |
| Groove-filling haunch | Match groove | Frame-and-panel work | Small haunch fills the plow | Keep the haunch slightly shorter than groove depth. |
| Stub tenon | Short bearing | Light frames and dividers | Small shoulder cleanup | Use for alignment, not heavy racking loads. |
| Project | Rail size | Receiving member | Tenon target | Fit note |
|---|---|---|---|---|
| Cabinet door rail | 3/4 by 2-1/4 in | 3/4 in stile | 1/4 by 1/2 in | Haunch hides the panel groove. |
| Table apron | 3/4 by 3-1/2 in | 1-1/2 in leg | 1/4 to 5/16 by 1 in | Shoulders on all four sides help resist racking. |
| Bed rail | 1-1/2 by 5-1/2 in | 2-1/2 in post | 5/8 by 1-1/2 in | Use hardware or drawbore only with enough back wall. |
| Chair stretcher | 5/8 by 1-1/4 in | 1-1/4 in leg | 3/16 to 1/4 by 3/4 in | Cyclic loads need a clean shoulder fit. |
| Workbench base | 1-1/2 by 4 in | 3 in post | 5/8 by 1-3/4 in | Deep mortise with a solid back wall. |
Balanced through layout
Best for: cabinet doors, face frames, and most table aprons.
The one-third rule leaves cheek strength and enough shoulder to hide small fitting gaps.
Haunched tenon
Best for: frame-and-panel doors or rails with grooves.
The haunch fills the groove and reduces twist near the rail end without making the mortise full-width.
Drawbored tenon
Best for: heavy benches, beds, and knockdown-looking traditional frames.
Offset pulls the shoulder tight, but the tenon and post need enough thickness around the peg hole.
Stub tenon
Best for: dividers, light doors, and alignment joints.
Fast and clean for light work, but it gives less long-grain glue area and less racking resistance.
Fit the mortise to the tool, then tune the tenon: if a chisel or router bit sets the mortise width, plane the tenon cheeks to a light slip fit instead of widening the mortise by eye.
Keep shoulders doing real work: side shoulders register the rail, face shoulders hide tiny cheek gaps, and a small glue-relief space at the mortise bottom prevents hydraulic lock.
A mortise and tenon joint is a method of joining two pieces of wood together in a way that creates a joint that is stronger than the pieces of wood that are being joined. The strength of a mortise and tenon joint is dependent upon the proportions of the joint, and the proportions of the joint must match the specific loads that the joint will experience. A calculator can help to determine those proportions for a joint based off the dimensions of the pieces of wood that will be joined.
One of the primary inputs into the calculator is the thickness of the rail. The thickness of the rail will impact all of the other dimensions of the joint. For instance, a person may set the thickness of the rail to 3/4” thick, which would indicate to another person that the tenon should be 1/3 of that thickness.
How to Use a Mortise and Tenon Calculator
However, the calculator will adjust the thickness of the tenon based upon the specific type of load that is to be placed upon the joint. For instance, a cabinet door will have a thinner tenon than a bed rail or workbench stretcher. Additionally, the type of wood used for the tenon will also impact the thickness of the tenon; hard woods like oak or maple will allow for thinner walls around the mortise than soft woods like poplar or pine.
Another variable that must be considered is the length of the tenon. The length of the tenon impacts the amount of glue that will be placed between the tenon and the mortise, and the amount of wood that remains after cutting the tenon. The calculator will compare the length of the tenon to the thickness of the stile or post upon which the tenon will be placed.
If the length of the tenon would leave a back wall that is too thin, the calculator will lower the joint score and warn the user. Additionally, if the length of the tenon creates a mortise that is too close to the face of the wooden member that is to be joined, the calculator will lower the score of the joint. If the joint includes a haunch, the program will adjust the length of the tenon so that it accounts for the loss of long grain glue area created by the haunch.
Another dimension that must be considered is the width of the shoulders. Shoulders are used to allow the rail to be properly located within the stile, and to hide the gaps between the cheeks of the tenon. The width of the shoulders will impact the location of the rail, so the width of the shoulder must be selected carefully.
The calculator will provide both the width of the side shoulders and the face shoulders. If the width of the shoulders is too small, there wont be enough room for error in cutting the wood to the proper size. Thus, if the width of the shoulders is too small, the calculator will provide a lower joint score and suggest a thicker tenon.
Additional inputs into the calculator are the amount of glue clearance and the drawbore offset of the joint. Glue clearance is provided to allow for the tenon to not bind to the mortise prior to the shoulders of the tenon are placed into the mortise. The amount of glue clearance will be based upon the type of wood that is to be utilized in the joint; denser woods will require less glue clearance than less dense woods.
Drawbore offset is introduced as a means of providing a pull on the joint to fully seat the joint. However, if the joint will be made out of brittle wood, or if the thickness of the receiving member is thin, the calculator will limit the drawbore offset in the recommendations to avoid splitting the wood. The tables located on the calculator provide additional information regarding the types of mortise and tenon joints that are made, and the sizes of each of the components of those joints.
The tables can provide an understanding of the typical tenon thicknesses for different sizes of rails, and the depth of the mortise that should be created based upon the thickness of the stile. The tables can provide general information about the types of dimensions that are typically used for mortise and tenon joints, and will help the woodworker understand if the dimensions created by the calculator are in the range of those typical dimensions. The use of the calculator will force the woodworker to make decisions regarding the type of mortise and tenon joint that will be created.
For instance, the dimensions of a joint that is to be used for a drawer divider will be different than a joint that is used for a frame and panel door. For instance, a stub tenon will have different dimensions than a haunched tenon. Additionally, different loads will require different drawbores for the tenons.
Thus, the calculator will assist the woodworker in making these decisions, and ensure that the resulting dimensions match the types of loads that are to be placed upon the joint. For instance, if the joint score is low due to the thin back wall, the tenon should be shortened or the stile should be thicken. Many woodworkers make mistakes that treat each dimension of a tenon joint as independent of the other dimensions.
For instance, a woodworker may set the length of a tenon based upon a rule of thumb, without ensuring that there is enough material remaining in the piece of wood behind the mortise to cut the tenon. Additionally, the size of a haunch may be selected without realizing that the haunch will reduce the long grain glue area of the joint. Additionally, a drawbore may be selected based upon another project that was made, without realizing that the wood for this project is more brittle than the wood that was used for the other project.
Thus, the calculator allows a woodworker to see these potential mistakes prior to beginning to cut the wood. One of the main uses of the calculator is to allow a woodworker to test the layout of the joint upon scrap wood. By cutting a test joint according to the dimensions that are created by the calculator, a woodworker can ensure that the joint will fit properly into the mortise.
If the test joint does not fit properly, the breakdown of the calculator will indicate which dimension requires adjustment. Thus, by testing the joint upon scrap wood, a woodworker can create a reliable workflow for cutting the actual pieces of wood that are to be joined by mortise and tenon joints. Each of the numbers that is provided by the calculator are important to the function of the joint.
Each joint relies upon the long grain of the wood to meet the long grain of the wood under compression. Each joint relies upon the shoulders to properly register the two portions of the joint, and each joint must provide enough material behind the mortise to resist any pulling forces that are placed upon the joint. Thus, the calculator makes visible to each woodworker the relationship between each of the dimensions of the joint, and allows the woodworker to build the joint with knowledge of the relationship between each of the dimensions.
