Table Leg Calculator

Table Leg Calculator for straight, splayed and X legs. Enter table height, top thickness, apron and stock size to find leg length, cut angles, knee clearance and the full cut list.

How the Table Leg Calculator Finds Leg Length

A straight leg runs from the underside of the top to the floor. Its length is the finished table height minus the top thickness, and glides or casters shorten the wood leg by their own height.

$$L=H-T-G$$

Here $L$ is the wood leg length, $H$ the height to the top surface, $T$ the top thickness and $G$ the glide or caster height, all in inches. A 30 in table with a 1-1/2 in top and no glides needs 28-1/2 in legs. Add 3/4 in glides and each leg drops to 27-3/4 in.

The usual slip is entering the nominal thickness of the top. An 8/4 board often surfaces to about 1-3/4 in, and that missing 1/4 in lands straight on the leg length. Leg stock works the same way, since a 4x4 is 3-1/2 in actual, and the calculator expects the actual size.

Table heights from 8 to 60 in are accepted, which covers coffee tables through bar and workbench heights. For a desk, the Ergonomic Desk Calculator finds a working height from your own body size, and that number becomes the table height here.

Knee Room Under the Apron

The apron does not change a straight leg's length, but it decides how much room your knees get. The Table Leg Calculator measures this from the floor to the underside of the apron.

$$C=H-T-A$$

The 2010 ADA Standards set accessible dining surfaces between 28 and 34 in high in section 902.3. Section 306.3 then asks for 27 in of knee height and 30 in of knee width below them. These rules govern accessible seats in public places, not a table built for your own home.

They still expose a real design conflict. On a 30 in table with a 1-1/2 in top, the apron can be no deeper than 1-1/2 in if you want 27 in of knee height. The default 4 in apron leaves 24-1/2 in, and the knee card flags it as 2-1/2 in short.

Raising the table helps more than most builders expect. At the 34 in ADA maximum, the same top allows an apron up to 5-1/2 in deep. The 30 in width rule is a leg spacing question the tool leaves to you, so keep at least 30 in clear between legs at any seat meant to be accessible.

Seat count follows the NKBA Kitchen Planning Guidelines, which allow 24 in of table edge per diner. They also scale knee depth with height, from 18 in at a 30 in table to 15 in at a 36 in counter and 12 in at a 42 in bar. A 72 in table seats three per long side, with 32 in clear behind each chair when no one walks past.

Tapering the Two Inside Faces

Traditional tapered legs lose wood only on the two inside faces, starting where the bottom of the apron meets the leg. Fine Woodworking gives this as the basic rule, because it keeps the joint area square.

Cut the apron joints while the stock is still square, and use the Mortise and Tenon Calculator to size them. The taper then runs from the apron line to the foot, so its length is the leg length minus the apron height.

$$\theta =\arctan \left(\frac{w-f}{L-A}\right)$$

In this formula $w$ is the leg stock width and $f$ the foot width after tapering. A 2-1/2 in leg tapering to a 1-1/2 in foot below a 4 in apron loses 1 in per face over 24-1/2 in. That is a 2.3 degree taper, or 0.490 in of jig offset per foot of length.

How far to taper is a style choice with no standard behind it. Builders on Sawmill Creek report taking 1-1/2 in legs down to about 3/4 to 7/8 in at the floor. A member of the Canadian Woodworking forum proposes a foot two-thirds the size of the head, which puts 2-1/2 in stock at about 1-11/16 in.

The leg stock card adds your trim allowance to every leg and reports board feet from the actual width and thickness. Four 2-1/2 in square legs at 30-1/2 in rough length come to 5.30 bd ft, and the Board Foot Calculator handles the rest of the lumber order.

Splay, Rake and the Resultant Angle

Splayed legs lean outward in one view or two. The calculator takes splay as the lean seen from the side of the table, toward the ends, and rake as the lean seen from the end, toward the sides.

Chairmakers often use those names the other way round. Lost Art Press describes splay in the front elevation and rake in the profile. The names do not change the math, so enter each angle in the view the label describes.

With both angles set, the leg leans along one line called the sightline, at a single angle called the resultant. The Table Leg Calculator uses the standard chairmaking trigonometry, with $V$ as the vertical drop from the underside of the top.

$$R=\arctan \sqrt{{\tan }^{2}s+{\tan }^{2}r}$$

$$\alpha =\arctan \left(\frac{\tan r}{\tan s}\right)$$

$$L_s=V\sqrt{1+{\tan }^{2}s+{\tan }^{2}r}$$

At 8 degrees of splay and 8 of rake, the resultant is 11.2 degrees along a 45 degree sightline. The leg grows from 28-1/2 to 29.06 in along its centerline, and each foot moves out about 4 in both ways. A 14 degree splay with 12 degrees of rake gives an 18.1 degree resultant on a 40.4 degree sightline.

Level cuts at the top and foot of a leaning square leg reach past the centerline length at the corners. The calculator adds that extra to the rough blank, so the stock is never cut short. Lost Art Press puts typical leg angles at 5 to 15 degrees, and the tool warns above a 15 degree resultant because the feet start reaching past the top edge.

A round leg fits a hole bored at the resultant angle in one setting. A square leg whose faces stay square to the aprons needs a compound miter and bevel instead, which the tool points out whenever both angles are above zero.

X Leg Angles From the Table Leg Calculator

X legs are where most builders get stuck, and board width is the reason. The angle depends on the rise, the width at the floor and the width of each board, because a wider board needs a longer level cut at the foot.

The rise $H_x$ is the table height minus the top, glides and top rail. The foot cut is $b/\sin \theta$ long, and the outer edge of each board climbs $H_x$ across whatever floor width is left after that cut.

$$\tan \theta =\frac{H_x}{W-b/\sin \theta }$$

Because $\theta$ appears on both sides, the Table Leg Calculator solves it by iteration. A LumberJocks thread reaches the same relationship from the foot triangle, and members there stress that leaving out board width gives the wrong angle.

Everything else follows from the angle. Each long edge is $H_x/\sin \theta$, the board is $b/\tan \theta$ longer tip to tip, and the miter saw is set to $90-\theta$. The half-lap where the pieces cross is $b/\sin 2\theta$ long and half the stock thickness deep.

The table below holds a 30 in table, 1-1/2 in top, 4 in rail and 28 in X width fixed, for a 24-1/2 in rise, and changes only the square stock size.

Stock size alone moves the angle about 3 degrees here. Treating each board as a line from corner to corner gives 41.2 degrees, almost 4 degrees off the 2-1/2 in answer, which is enough to leave the top rocking on its rail.

The tool counts each board as one piece, so a table with two X ends is 4 pieces, and it assumes two full-length boards joined by a cross-lap. The Lap Joint Calculator sizes that joint. Builders who butt two short pieces against one long board need different short-piece lengths than the ones shown.

X widths from 6 to 120 in are accepted, and an X too narrow for its stock returns an error instead of a length. Below 35 degrees from the floor the tool warns about racking, since the legs act as long levers on the lap. Real stiffness still varies with species, moisture content and how well the lap is glued, so treat that warning as a design check rather than a load rating.

What Woodworkers Ask About Table Legs

How thick should table legs be?

Leg thickness is rarely about carrying weight. In a LumberJocks thread asking for a leg size calculator, experienced members explain that wood is so strong along the grain that a leg is hard to make too thin for vertical load.

Sideways racking is the real test, and aprons, stretchers and solid joinery handle it. That is why the stock presets are about proportion, from 1-1/2 in for light tables up to 3-1/2 and 5-1/2 in for trestle and farmhouse builds, all as actual sizes.

What angle do you cut X legs?

No single angle works, because the rise, the floor width and the board width all change it. For a 30 in table with a 1-1/2 in top, a 4 in rail and a 28 in wide X in 2-1/2 in stock, the legs sit at 45.0 degrees and the saw is set to 45.0 degrees.

Make the X taller than it is wide and the leg angle climbs past 45 degrees while the saw setting drops below it. Miter saw scales read from a square cut, which is why the Table Leg Calculator gives $90-\theta$ as the setting instead of the leg angle itself.

How long should legs be for a 30 inch dining table?

Subtract the top thickness and any glide height from 30 in. A 3/4 in plywood top needs 29-1/4 in legs, a 1 in top needs 29 in, and a slab that surfaced to 1-3/4 in needs 28-1/4 in.

The Heights and Clearances table in the tool repeats this for 18 to 42 in tables using your own top and apron. It also marks which heights pass both ADA checks and which NKBA knee depth applies to each one.

Where should the taper start on a table leg?

Most builders start it at the bottom of the apron, which is where the calculator measures from. Some leave about an inch of square stock below the apron so the shoulder stays crisp, and a table with a lower shelf often starts the taper below the shelf instead.

Starting lower shortens the taper run, so the real angle and jig offset come out slightly steeper than the taper card shows. On a 24-1/2 in run, starting 1 in lower turns 0.490 in per foot into 0.511 in per foot for the same foot size.