Router Bit Passes & Depth Calculator
Determine the number of passes needed for a deep cut.
When using a router to make deep cuts, such as for mortises, dados, or deep profiles, making the cut in a single pass is often impossible and always dangerous. It puts excessive strain on the router, the bit, and the workpiece, leading to poor cut quality, burning, and a high risk of kickback.
The correct approach is to make several shallower passes, incrementally increasing the depth of cut. This calculator helps you determine the exact number of passes required based on your desired total depth and the maximum depth your bit can safely remove in a single pass. This ensures a safer operation and a cleaner final result.
The calculation is a simple division, rounded up.
- Determine Total Depth: Measure the final depth of the groove, dado, or profile you want to cut.
- 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".
- 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.
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Always double-check your measurements before cutting.
Account for the kerf (the width of the saw blade) in your calculations.
Consider wood movement (expansion and contraction) in your final dimensions.
Buy 10-15% extra material to account for mistakes and waste.