How to use the drawer box size calculator
- Pick inches or millimeters and enter the width, height and depth of the cabinet opening.
- Enter the side clearance and height clearance your drawer slides call for. These come from the slide data sheet.
- Leave the slide length blank to use the longest slide in the example list that fits, or enter the length you will buy.
- Enter the thickness of the box wood and the depth of the groove for the bottom, then read the box size and the cut list.
Formula
Box width = opening width - side clearance (both sides together)
Box height = opening height - height clearance
Box depth = slide length (the longest that fits the opening depth)
Front and back length = box width - 2 x side thickness; bottom = inside size + 2 x groove depth
The front and back sit between the sides, and the bottom panel rests in a groove cut in all four pieces. A different joint changes the lengths of the front and back.
A 20 inch wide opening with 1 inch slide clearance
For an opening 20 in wide, 6 in tall and 22.5 in deep, with 1 in of side clearance and 1 in of height clearance, the box is 19 in wide and 5 in tall. The longest slide in the example list that fits is 22 in, so the box is 22 in deep.
With sides 0.5 in thick and a 0.25 in groove, the sides are 22 x 5, the front and back are 18 x 5, and the bottom panel is 18.5 x 21.5. In millimeters, a 500 mm wide opening with 26 mm of side clearance gives a box 474 mm wide, and a 520 mm deep opening takes a 500 mm slide.
Clearances come from the slides
Side mount ball bearing slides usually need about half an inch on each side, while undermount slides need less at the side and more below. Because makers differ, the page has no built-in value. Enter what the data sheet says for your slide. The slide length list is only an example of common sizes.
Once the box is sized, the cabinet door size calculator helps with the front, and the board foot calculator estimates the lumber you need.
Checking the cut list
Dry fit the first box before cutting the rest. Measure the opening at the front, middle and back, because cabinets are rarely square, and use the smallest width. The cut list assumes a plain box joint with the front and back between the sides, so adjust the front and back length if you use rabbets or dovetails.
Assumptions and limits
- Clearances are totals for both sides (width) and for top and bottom together (height), taken from your slide data sheet.
- The box depth equals the slide length, and the list of slide lengths is an example, not a product catalog.
- The front and back fit between the sides, and the bottom sits in a groove in all four pieces.
- Drawer fronts, handles and rear clearance for the cabinet back are not included.
Frequently asked questions
How do I size a drawer box for a cabinet opening?
Subtract the total side clearance your slides need from the opening width, and the height clearance from the opening height. A 20 in opening with 1 in of clearance gives a 19 in wide box.
How much clearance do drawer slides need?
It depends on the slide. Side mount slides often need about 1 inch in total across the width, and others differ, so use your slide data sheet. The page asks you to enter the figure.
What size should the drawer bottom be?
The inside width and depth of the box plus two groove depths in each direction. With 0.5 in sides and a 0.25 in groove, a 19 x 22 box needs a 18.5 x 21.5 bottom.
How deep should the drawer box be?
Match the slide length, which is the longest slide that fits within the opening depth. A 22.5 in opening takes a 22 in slide.