Furniture Design Calculators

Calculate shelf span and sag, drawer and slide dimensions, table and chair proportions, and ergonomic heights - design pieces that fit and hold.

Bed Frame CalculatorBed Frame Calculator fitting a wood frame to your real mattress, with rail cuts, slats within Purple or Tempur-Pedic gap…Bookcase CalculatorBookcase Calculator that turns outside case size into even shelf spacing, floor marks, a cut list, 4x8 sheet count, book…Cabinet Door CalculatorCabinet Door Calculator sizing each door from the opening for overlay, inset or frameless cabinets, then listing stile, rail and…Chair Angle CalculatorChair Angle Calculator turning rake and splay into the sightline and resultant to bore at, corrected for seat tilt, with…Drawer Box CalculatorDrawer Box Calculator that fits a box to its cabinet opening by Accuride or Blum specs, with its full list…Drawer Pull Positioning CalculatorDrawer Pull Positioning Calculator giving drill marks from the front edge, a pull size by the one-third rule, and the…Ergonomic Desk CalculatorErgonomic Desk Calculator that sets a chair seat, desk top and screen to fit your height, using military body-size data…Hinge CalculatorHinge Calculator giving the hinge count, cup boring and overlay for Blum cabinet hinges, plus the butt hinge size, count…Shelf Span CalculatorShelf Span Calculator that gets midspan sag in panel and solid wood shelves, plus the longest span, the load at…Table Leg CalculatorTable Leg Calculator that finds straight leg length, inside taper, splay resultant and X leg miter angle, then tests if…

Furniture Design Calculators

Good furniture is proportion plus physics. A piece has to look right and hold up under real use. Guess the numbers and a shelf sags, a drawer binds, or a table tips when someone leans on it. These calculators give you the dimensions that make a piece both balanced and sound.

Shelf span and sag

Shelf span is the number people get wrong most. A shelf that looks fine empty bows once it's loaded with books. Span limits depend on material and load. Under a full run of books, 3/4-inch plywood holds a clean span up to about 30 inches. Solid oak of the same thickness reaches closer to 36.

Push past that and the sag shows. Our shelf sag calculator works the span from your material, thickness, and load, so you know where to add a support or thicken the stock before you build.

Drawers, doors, and slides

Drawers live or die on clearance. Standard side-mount slides need about 1/2 inch of space on each side, and the gaps between drawer fronts should stay even for a clean look. Our drawer and slide calculators size the box, set the slide clearance, and space the fronts, so the drawer runs smooth and the front looks deliberate. Cabinet door tools work out overlay and hinge placement the same way.

Proportion and ergonomics

Proportion is what makes a piece look right before you can say why. Many makers lean on the golden ratio - roughly 1 to 1.618 - for the relationship between a piece's height, width, and depth. Ergonomics sets the rest: seat, desk, and table heights that fit the body using them. Our proportion and height tools turn those rules into working dimensions for your build.

Sag and stability shift with wood species, moisture, and how a piece is loaded, so treat these as design starting points - build in a margin and add a support or back panel where a span runs long.