Bit Size For Inch And A Half Plumbing: The Ultimate Guide

Have you ever stared at a wall, drill in hand, only to realize you’re not sure if that 1.75-inch hole saw is actually going to fit your 1.5-inch pipe? It is a frustratingly common mistake that can ruin drywall or leave you with gaps that are impossible to seal properly. Understanding the correct bit size for inch and a half plumbing is essential for a clean, professional-looking installation that stands the test of time.

In this guide, we will break down the exact measurements, the difference between nominal and actual sizes, and the best tools to use for copper, PVC, and PEX pipes. Whether you are a seasoned DIYer or a beginner tackling your first bathroom remodel, getting this measurement right is the foundation of leak-free and code-compliant work.

Why Nominal Size Is Not Actual Size

Before we dive into the specific drill bits, it is crucial to understand why “1.5 inches” is a misleading term in the plumbing world. In plumbing, pipe sizes are referred to as “Nominal Pipe Size” (NPS). This is a historical standard that does not reflect the actual outer diameter (OD) of the pipe.

For a 1.5-inch pipe, the actual outer diameter varies depending on the material:

• Copper (Type L/M): Approximately 1.625 inches (1-5/8″).
• PVC (Schedule 40): Approximately 1.900 inches.
• PEX Tubing: Varies by brand, but generally close to 1.625–1.660 inches for 1.5-inch nominal.

If you use a 1.5-inch drill bit, your pipe simply will not fit. If you guess too large, you create structural weaknesses in your framing and make insulation difficult. This discrepancy is why knowing the precise bit size for inch and a half plumbing is non-negotiable for quality workmanship.

What Is the Correct Drill Bit Size for 1.5-Inch Pipes?

The “correct” bit size depends entirely on two factors: the material of the pipe and whether you need a tight fit or a loose fit for expansion.

For Copper Pipes (1.5-Inch Nominal)

Copper pipes have an outer diameter of roughly 1.625 inches. However, you never want to drill a hole exactly the same size as the pipe. You need clearance for:

1. Minor imperfections in the wood stud.
2. Expansion and contraction due to temperature changes.
3. Ease of installation.

Recommended Bit Size: Use a 1-3/4 inch (1.75″) spade bit or hole saw.

• Why? This provides about 1/8 inch of clearance on all sides, which is the industry standard for rigid pipes like copper.

For PVC Pipes (1.5-Inch Nominal)

PVC Schedule 40 pipe has a significantly larger outer diameter of 1.900 inches. A 1.75-inch bit will be far too small.

Recommended Bit Size: Use a 2-inch hole saw.

• Why? A 2-inch hole provides approximately 1/16 inch of clearance on each side. This is tight enough to maintain fire-blocking integrity but loose enough to slide the pipe through without forcing it.

For PEX Pipes (1.5-Inch Nominal)

PEX is flexible, but when running through studs, it is often supported by rigid manifolds or requires protection from nails/screws.

Recommended Bit Size: Use a 1-3/4 inch (1.75″) bit.

• Note: Since PEX can expand more than copper, some plumbers prefer a 2-inch bit for long runs to prevent friction noise (“water hammer” vibrations against the wood), but 1.75 inches is generally acceptable for standard residential runs.

Comparison Table: Pipe Material vs. Drill Bit Size

Data sourced from standard ASTM piping dimensions.

Step-by-Step: How to Drill Perfect Holes for Plumbing

Drilling through studs requires precision to maintain the structural integrity of your home. Follow these steps to ensure safety and accuracy.

Step 1: Locate and Mark the Studs

Use a stud finder to locate the center of the studs. Mark the center line vertically with a pencil. According to building codes, holes should generally be drilled in the center third of the stud’s height to avoid weakening the load-bearing capacity.

Step 2: Choose the Right Tool

• Spade Bits: Best for quick, rough holes in softwood. They are cheap and fast but can tear out the wood on the exit side.
• Auger Bits: Better for deep drilling as they pull chips out efficiently.
• Hole Saws: Essential for PVC or when you need a perfectly clean, round hole. They are slower but produce the least amount of tear-out.

Step 3: Drill from Both Sides (Pro Tip)

To prevent the wood from splintering on the back side of the stud:

1. Drill halfway through from one side until the pilot point emerges on the other.
2. Flip to the other side and align your bit with the emerging point.
3. Complete the hole from the second side. This technique ensures a clean entry and exit, which is vital if you are installing escutcheon plates later.

Step 4: Deburr and Inspect

After drilling, check the hole for sharp wood splinters. Use a utility knife or sandpaper to smooth the edges. Sharp edges can cut into PEX tubing or damage the protective coating on copper pipes over time.

Important Code Considerations and Safety

When modifying framing for plumbing, you must adhere to local building codes and the International Residential Code (IRC).

1. Hole Diameter Limit: The diameter of the hole should not exceed one-third of the depth of the stud. For a standard 2×4 stud (which is actually 3.5 inches deep), the maximum hole size is roughly 1.16 inches.
   • Wait, what? You might notice that a 1.75-inch hole exceeds this limit for a 2×4. This is why 1.5-inch plumbing lines are rarely run through standard 2×4 interior walls without special consideration.
   • Solution: For 1.5-inch pipes, you often need to use 2×6 studs, notch the plate (if allowed by code), or route the pipe around the framing. Always consult a structural engineer or local inspector if you are cutting large holes in load-bearing walls. Learn more about structural framing standards on Wikipedia.
2. Edge Distance: Keep holes at least 2 inches away from the edge of the stud to prevent splitting and maintain nail-holding strength for drywall.
3. Fire Blocking: If you are drilling through multiple floors, you may need to install fire blocking around the pipe penetrations to prevent the spread of flames and smoke.

Common Mistakes to Avoid

• Using the Wrong Bit Type: Using a wood bit on metal studs will destroy the bit. Use step bits or hole saws designed for metal when working with steel framing.
• Ignoring Pipe Insulation: If you plan to insulate the pipe, you must account for the insulation thickness. A 1.5-inch copper pipe with foam insulation may require a 2.5-inch or 3-inch hole. Measure the insulated diameter first!
• Drilling Too Close to Plates: Never drill within 1.5 inches of the top or bottom plate of the wall frame unless specifically reinforced.

FAQ: Frequently Asked Questions

1. Can I use a 1.5-inch drill bit for 1.5-inch plumbing?

No. A 1.5-inch drill bit is smaller than the actual outer diameter of almost all 1.5-inch nominal pipes. Even copper pipe is 1.625 inches wide. You will not be able to fit the pipe through the hole.

2. What size hole do I need for 1.5-inch PVC?

You need a 2-inch hole saw. PVC Schedule 40 has an outer diameter of 1.900 inches. A 2-inch hole provides the necessary clearance for easy installation without compromising the stud’s integrity too much.

3. Does it matter if I use a spade bit or a hole saw?

Yes. Spade bits are faster and cheaper but leave rougher edges. Hole saws create cleaner, more precise rounds which are better for sealing air leaks and fitting escutcheon plates. For PVC, always use a hole saw to prevent cracking the pipe on rough wood edges.

4. How do I handle 1.5-inch pipes in 2×4 walls?

This is tricky because a 1.75-inch hole exceeds the 1/3 rule for 2×4 studs. Options include:

• Running the pipe along the face of the studs (furring out the wall).
• Using 2×6 studs for that specific wall section.
• Notching the studs (only if permitted by local code and not in load-bearing zones). Always check with your local building department.

5. Should I leave space for pipe expansion?

Absolutely. Pipes expand and contract with temperature changes. A tight fit can cause squeaking noises or stress on joints. Always allow at least 1/8 inch of clearance around rigid pipes like copper and PVC.

Conclusion

Getting the bit size for inch and a half plumbing right is about more than just making the pipe fit; it’s about ensuring the longevity, safety, and professionalism of your project. Remember the golden rules: 1-3/4 inch for copper/PEX and 2 inch for PVC. Always account for insulation, respect structural limits, and drill cleanly to protect your pipes.

By following these guidelines, you avoid costly reworks and ensure your plumbing system remains secure and quiet for years to come. If you found this guide helpful, please share it with your fellow DIY enthusiasts on social media or save it for your next renovation project!