The calculation is a simple division, rounded up.

1. Determine Total Depth: Measure the final depth of the groove, dado, or profile you want to cut.
2. Determine Max Depth Per Pass: This is a crucial value. A common rule of thumb is to not remove more material than half the diameter of the router bit in a single pass. For a 1/2" bit, the max depth per pass would be 1/4".
3. Calculate Passes: The calculator divides the total depth by the max depth per pass and rounds up to the nearest whole number to get the required number of passes.
   Passes = Ceiling( Total Depth / Max Depth per Pass )

• Pass: A single cutting operation with the router at a specific depth.
• Depth of Cut: The amount of material being removed by the router bit in a single pass.
• Router Bit Diameter: The cutting diameter of the router bit. A key factor in determining the max depth of cut.
• Burning: Scorching of the wood caused by excessive friction, often from too deep a cut or too slow a feed rate.

Example 1: A 3/4-inch dado with a 1/2-inch bit.
Half the 1/2-inch bit's diameter caps each pass at 1/4 inch, so 0.75 / 0.25 = 3 passes. Set the fence once and lower the depth a quarter-inch each time.

Example 2: A 1/2-inch mortise with a 1/4-inch bit.
A 1/4-inch bit only safely takes 1/8 inch per pass, so 0.5 / 0.125 = 4 passes. Small bits need more, lighter bites — not fewer, deeper ones.

Example 3: A 1-inch deep rabbet at 3/8 inch per pass.
1.0 / 0.375 = 2.67, and because you cannot make a partial final pass, the calculator rounds up to 3 passes. That last pass removes just 1/4 inch.

• Rounding Down: You can't finish a depth with a fraction of a pass. Any remainder means one more full setup step — the calculator always rounds up for that reason.
• Exceeding Half the Bit Diameter: Taking deeper bites than the bit can clear packs chips, burns the cut, and risks snapping the bit.
• Same Depth for Every Material: Hard maple and MDF demand shallower passes than pine. Adjust the per-pass number to the stock, not just the bit.
• Plunging Into a Deep Dado in One Go: Dropping straight to final depth in a closed pocket is a classic stall-and-kickback setup. Ratchet down in calculated steps.

"I set my depth with one or two test passes in scrap and mark the router's turret stop, rather than trusting a tape. It is far faster to lower a quarter-inch between passes than to fix a burned, blown-out groove." - Cabinet Shop Router Operator

"Chip clearance is the hidden half of depth. A deep, narrow pocket needs you to lift and clear the flutes between passes even when the math says the depth is safe — packed chips are what actually burn and break bits."

• Dado grooves: Shelf and cabinet joinery cut across the grain in multiple shallow bites.
• Routed mortises: Deep end-pocket cuts in legs and rails that must be ratcheted down.
• Template profiling: Flush-trim or pattern cuts that reach full thickness a pass at a time.