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Calcimator

Mortise and Tenon Calculator

Joint dimensions, peg sizing, and shear capacity from timber size and load using traditional timber framing rules.

Inputs

in
in
in
lbs

Results

Tenon thickness

2.5 in

Tenon width

6 in

≈ 2 credit cards

Tenon length6 in
Mortise depth6.25 in
Mortise wall thickness2.75 in
Shoulder depth1 in
Peg diameter0.88 in
Minimum relish1.75 in
Draw-bore offset0.06 in
Tenon shear capacity12,960 lbs
Shear utilization ratio0.15
How to Use This Calculator
  1. Enter Tenon timber width, Tenon timber depth, and Mortise timber width.
  2. Set Applied joint load and Wood species.
  3. Review Tenon thickness (in) and Tenon width (in).
  4. Use Tenon length (in) and Mortise depth (in) to inform your decision.

How the result changes with Tenon timber width

Tenon timber widthTenon thicknessTenon width
5.21.5 in6 in
8.22.5 in6 in
124 in6 in
155 in6 in

What each input means

Tenon timber width
Width of the timber that will have the tenon cut into it.
Tenon timber depth
Depth (height) of the timber that will have the tenon.
Mortise timber width
Width of the timber receiving the mortise (tenon inserts into this).
Applied joint load
Force the joint must resist (gravity load or lateral load).
Wood species
0 = Douglas Fir-Larch, 1 = Southern Pine, 2 = Eastern White Pine.

What each result means

Tenon thickness
Recommended tenon thickness (≈ 1/3 timber width).
Tenon width
Tenon width (timber depth minus 1 in shoulder each side).
Tenon length
How far the tenon extends into the mortise (≈ 3/4 receiving width).
Mortise depth
Mortise depth (tenon length + 1/4 in clearance).
Mortise wall thickness
Wood remaining on each side of the mortise in the receiving timber.
Shoulder depth
Shoulder dimension on each side of the tenon.
Peg diameter
Recommended hardwood peg diameter (≈ 1/3 tenon thickness, min 3/4 in).
Minimum relish
Minimum wood beyond the peg hole to prevent splitting (2× peg diameter).
Draw-bore offset
Typical offset between tenon and mortise peg holes for draw-boring.
Tenon shear capacity
Maximum shear load the tenon cheeks can resist.
Shear utilization ratio
Applied load / shear capacity. Must be ≤ 1.0.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Tenon timber width = 8, Tenon timber depth = 8, Mortise timber width = 8, Applied joint load = 2000 = 5 input(s) provided
  2. Calculate Tenon thickness
    Tenon thickness = max(1.5, round(rawTenonThickness * 2) / 2)
    2.5 = 2.5
  3. Calculate Tenon width
    Tenon width = max(2, timberDepthIn - 2)
    6 = 6
  4. Calculate Tenon length
    Tenon length = max(2, round(receivingWidthIn * 0.75 * 2) / 2)
    6 = 6
  5. Calculate Mortise depth
    Mortise depth = tenonLength + 0.25
    6.25 = 6.25

Engine last updated . Checked against 2 independently-derived tests — how we verify calculators.

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