A dado width calculator solves one of the most common cabinet and furniture frustrations: nominal 3/4" plywood is rarely actually 3/4". If you cut your dado to 0.750", the panel will be sloppy or not fit at all. This tool gives you the precise width to cut based on actual measured plywood thicknesses and your preferred fit tolerance.
Calculate Dado Width
Enter material thickness and fit preference to calculate dado width.
Common Plywood Actual Thicknesses
| Nominal Size | Typical Actual | In mm |
|---|---|---|
| 1/4" (6mm) | 7/32" (0.218") | 5.5mm |
| 1/2" (12mm) | 15/32" (0.469") | 11.9mm |
| 3/4" (18mm) | 23/32" (0.703") | 17.9mm |
| 3/4" Baltic Birch | 18mm (0.709") | 18mm |
| 3/4" MDF | 3/4" (0.750") | 19mm |
How to Calculate the Right Dado Width
Getting a precise dado width is critical for cabinet, bookcase, and furniture work. A dado that is too tight will crack the shelf panel when it expands. A dado that is too loose looks sloppy and creates a weak joint. The key insight is that you must work from the actual measured thickness of your material, not the nominal size.
Step 1: Measure Your Actual Material
Use digital calipers to measure the actual thickness of your plywood or solid wood. Do this for every new sheet or board — the same nominal size from different manufacturers or species can vary by 1-2mm. Measure in at least three places to account for variation across the sheet.
Step 2: Choose Your Fit Type
Snug fit (add 0.003") is ideal for glue-up applications where the shelf or panel is permanent. Slide fit (add 0.010") works for adjustable shelves, drawers, and anything that needs to move in and out. A slide fit dado is typically used in conjunction with shelf pins for adjustable shelving.
Step 3: Cut a Test Dado First
Always test your dado settings in scrap material of the same thickness before cutting your project pieces. Make the dado at your calculated width, then slide the panel in. If it is tight, add a paper shim (approximately 0.003") to the router fence. If it is loose, adjust in the opposite direction.
FAQ
Why is nominal 3/4" plywood actually thinner?
Plywood is manufactured to metric thicknesses and converted to imperial. Most 3/4" plywood is actually 23/32" (0.71875") or sometimes as thin as 11/16" (0.6875"). Baltic birch plywood is often closer to the nominal size. Always measure your actual material with calipers before routing a dado.
What is a snug fit vs slide fit vs loose fit for dados?
Snug fit: the panel slides in with light hand pressure but no slop — best for permanent glue-up. Slide fit: the panel slides in freely — good for removable shelves. Loose fit: obvious play in the joint — generally undesirable but acceptable for painted work where you are filling gaps. For most cabinet and shelving work, snug fit (0.002-0.005" clearance) is ideal.
How do I cut the exact dado width I need?
Router method: use a test piece of the same material and adjust the router's shim or use an adjustable dado jig until the fit is correct. Table saw dado stack: adjusting the number of chippers or adding paper shims between the blades. Always cut test dados in scrap wood first and check the fit before committing to your project.
What router bits work best for dados?
Straight bits or spiral upcut bits are most common for dados. Spiral upcut bits leave a cleaner bottom and eject chips better. For wide dados, multiple passes with a narrower bit are often cleaner than a single wide-cut. Pattern router bits with a fence or jig produce the most consistent results.
Is this dado width calculator free?
Yes, completely free with no signup required. All calculations run in your browser.