Hole Saw Sizes Explained: Common Sizes and How They Map to Pipe and Conduit

The pipe is stamped 1/2 inch, but the saw that actually fits it reads 7/8 inch. That gap is where most first cuts go wrong, whether you are running EMT through a panel or feeding a drain line into a wall. The chart below is hole saw sizes explained: common sizes and how they map to pipe and conduit. One rule drives every number on it, and the rule is this: the hole is drilled for the fitting that goes into it, never for the pipe’s label.

Why Doesn’t The Hole Saw Match The Pipe Label?

Trade size is a naming convention, not a measurement. A 1/2-inch conduit carries a nominal trade size that only loosely tracks its inside diameter, and the outside diameter runs larger still, shifting with wall thickness. The hole saw, by contrast, is sized to the opening a connector or knockout needs. That is the whole reason the two numbers never line up.

So the figure stamped on the saw describes the drilled hole, not the pipe. That hole has to clear the connector body, the locknut, or the pipe shoulder that seats into it. Measure the actual outside diameter with calipers, hold it against the fitting, and let the chart confirm your cut instead of trusting the trade size on its own.

The mismatch has real consequences. Drill too small and the connector will not seat, so you ream the hole wider with the saw and end up with an oval opening that strips the locknut’s bite. Drill too large and the connector wobbles, the seal fails, and the panel loses its grip on the run. Getting the number right the first time beats fixing a wallowed hole.

Hole Saw Sizes For Pipe And Conduit: What Decides The Cut

For US conduit, the drilled opening is what counts, and the mapping runs roughly one step above the trade size. These figures follow NEMA’s recommended hole and drill sizes, the reference most US electricians work from.

Read the chart as a wiring guide, not a law. The jump between sizes is not a fixed fraction, which is why guessing “add an eighth” falls apart at 3-inch and up. The 2-1/2-inch opening under 2-inch conduit is one of the most common cuts on a job, and if you are buying that size, a tested roundup of 2-1/2-inch hole saws can spare you a second trip to the store.

What About PVC, EMT, And Drain Pipe?

The conduit chart is not a universal pipe chart. EMT, rigid PVC, and plumbing drain pipe each use their own fitting families and tolerances, so an opening that fits one system can bind or rattle in the next. PVC also behaves differently under a bit, and general-purpose charts usually point to a PVC-specific or carbide-tipped cutter rather than assuming a bi-metal saw is ideal.

And trade sizes are not global. Metric conduit and international pipe standards use different outside diameters than the US trade sizes in the table, so a chart built for one system will steer you wrong on the other. Copper tubing follows its own naming too, sized by outside diameter, which makes any pipe-to-conduit shortcut risky.

Treat those as starting points, since fittings vary by brand.

Before any cut, pin down what the opening is for:

• Knockout — follows the punch size.
• Connector entry — follows the connector’s own body and thread.
• Pipe penetration — follows the pipe plus any clearance or insulation it carries.

Test the fit against the actual hardware first. When it’s right, the connector drops in flush with light pressure and the locknut spins on by hand, no hammering and no gap. One more trap: plenty of charts online list punch-equivalent sizes in the same column as hole saw diameters, and mixing those columns is how a perfectly good saw cuts the wrong opening.