What Size Hole Saw for 1 1/2 Pipe? Start With a 2-Inch Cutter

If you're running a 1-1/2-inch Schedule 40 PVC pipe through wood framing, use a 2-inch hole saw. If a Charlotte pipe PVC fitting hub — the socket end — has to pass through the same hole, go up to a 2-1/2-inch hole saw. If it's copper, pick a 1-3/4-inch hole saw. And if you're reaching for a 1-1/2-inch hole saw because the pipe is called 1-1/2 inches, stop. That is the exact mistake I made, and it cost me more in time than any ruler in my bag.

For the last 12 years I've handled Charlotte pipe and fittings orders and installations on both repair work and new construction. I've personally made, and written down, 18 avoidable sizing mistakes — roughly $11,000 in rework and wasted material by my count. I now keep the crew checklist that comes at the end of this article, mostly so the next person doesn't repeat my brilliant errors.

Why a 1-1/2-Inch Hole Saw Won't Fit a 1-1/2-Inch Pipe

Here is the part that confuses almost everyone the first time: the pipe size is not the pipe's outside diameter. It's a nominal size, which is another way of saying it's a label. The dimensional system used by most American pipe goes back to iron pipe standards, where the name referred to the approximate inside capacity of a standard wall pipe, not the physical outside measurement.

For 1-1/2-inch Schedule 40 PVC, the actual outside diameter is 1.900 inches. The inside diameter is around 1.61 inches. Neither number is 1.5. So when you cut a 1-1/2-inch hole, you're asking a 1.9-inch pipe to fit through a 1.5-inch opening. It doesn't matter how hard you push.

The first time I didn't believe this was in 2014, on a washer box drain line in a 2x6 wall. The pipe had 1-1/2 printed all over it, so I grabbed the matching hole saw. I pressed, pulled, and pressed again. The pipe wasn't going through. From the outside, it looked like I had simply drilled in the wrong spot. The reality is I drilled the right spot with the wrong diameter. There is no way to compensate by hitting harder.

Outside Diameter Cheat Sheet for 1-1/2-Inch Pipe

This is the list I keep in the van, and it's saved me more times than I can count:

• 1-1/2-inch PVC Schedule 40 / DWV: outside diameter 1.900 inches — hole saw: 2 inches
• 1-1/2-inch CPVC: outside diameter 1.900 inches — hole saw: 2 inches
• 1-1/2-inch copper: outside diameter 1.625 inches — hole saw: 1-3/4 inches
• 1-1/2-inch PEX (CTS): outside diameter roughly 1.625 inches — hole saw: 1-3/4 inches
• 1-1/2-inch galvanized or black iron: outside diameter 1.900 inches — hole saw: 2 inches

If I'm pre-planning a job, I keep the Charlotte pipe and fittings catalog nearby because it lists published dimensions for pipe and fittings. But no catalog replaces holding the actual part in your hand. A 30-second measurement with calipers beats a 30-minute trip back to the supply house.

The Hub Exception: Why Fittings Change the Answer

Now the part that still catches people, including me in 2022. A 2-inch hole lets the pipe slide through, but it will not let a fitting hub slide through. The socket end of a 1-1/2-inch PVC coupling or tee is noticeably fatter than the pipe itself. I've measured hub bodies anywhere from about 2.2 inches to 2.3 inches depending on the pattern and manufacturer. So a 2-inch opening is already too small, and a 2-1/4-inch opening is borderline at best.

I want to say the exact hub number varies too much to print a single figure, so don't quote me on one number. That's the point. If you need a hub or a complete fitting assembly to pass through the same opening, go with a 2-1/2-inch hole saw and check the widest point before you commit. When in doubt, measure the hub with a tape or caliper, add about an eighth of an inch, and buy that hole saw.

The lesson I learned the hard way: the pipe is not the only thing going through the hole. The fitting is part of the assembly, and the assembly has its own outside diameter.

When the 2-Inch Answer Is Wrong

Before you drill anything structural, check what you're drilling through. A 2-inch hole through a non-load-bearing partition is usually not a problem. A 2-inch hole through a load-bearing 2x4 stud usually is a problem. In common US residential framing rules, a hole in a load-bearing stud can't be more than about 40 percent of the stud depth. Forty percent of a 2x4 is about 1.4 inches, so 2 inches violates that limit. If you're working in a 2x6 wall, 2 inches is a different story, but local codes and engineered truss rules can still apply.

Also, don't cut into engineered I-joist flanges, and never assume a hole location is fine just because the bit fits. I-joist manufacturers publish web hole charts. Follow them. The same goes for fire-rated assemblies: a hole in a fire-rated wall usually needs a listed penetration seal, not just drywall and caulk.

And one more thing: if the pipe is insulated, the hole has to fit the insulation, not just the pipe. A half inch of foam on each side turns a 1.9-inch pipe into a roughly 2.9-inch object. The pipe might fit through a 2-inch hole; the insulation won't.

A Related Mistake: Grabbing the Wrong Wrench

Hole saws aren't the only place where I see people match the number on the pipe and grab the wrong tool. On threaded galvanized or black iron, I often see someone try to break loose a 1-1/2-inch fitting with a 10-inch pipe wrench. A 10-inch pipe wrench is a great tool for sink traps, valves, and tight cabinet spaces. On 1-1/2-inch threaded pipe, it just doesn't have enough reach. You end up forcing it, and that's how fittings crack or knuckles meet drywall.

For most work from half inch up to 2 inches, I carry a 14-inch pipe wrench. It's heavier than the 10-inch, but leverage beats strength. If I'm working overhead for most of the day, an aluminum 14-inch pipe wrench saves my arm without giving up much. The 10-inch still rides in the bag for the small stuff.

One rule I enforce with my crew: don't use a pipe wrench on PVC or CPVC fittings. A pipe wrench will gouge the surface and can crack a hub. For plastic pipe, use a strap wrench or your hands. The fitting is supposed to be glued, not crushed.

My Pre-Drill Checklist

Here is the checklist I wish someone had handed me in 2014:

1. Confirm the pipe material. PVC, copper, and steel all use different outside diameters for the same nominal size.
2. Measure the pipe's actual outside diameter with calipers. Don't trust the printed label.
3. Measure the fitting hub or coupling if it has to pass through the hole. The widest part of the assembly wins.
4. Add clearance for insulation, angled runs, or anything else that makes the effective diameter larger.
5. Check the framing member. Load-bearing studs, joists, and engineered lumber all have limits.
6. Wear eye protection and clean the burrs after cutting.

This sounds like a lot, but it takes about two minutes. Most of my expensive mistakes came from skipping the two minutes because I was sure the answer was obvious.

So the honest summary is short: pipe sizes are categories, not measurements. Measure the actual outside diameter, measure the fitting if it has to pass through, and add a little clearance. Do that, and any hole saw question becomes a lot easier.