What’s the Right Sink Drain Pipe Size and How Do You Measure It?
Get water down the drain faster with these tips
Highlights
The most common drain pipe sizes are 1 ¼ inches, 1 ½ inches, and 2 inches in diameter.
The size and type of sink will affect how big your drain pipe should be.
Improperly sized drain pipes can cause plumbing problems.
Your sink is only as good as the drain pipe it’s attached to. If the pipe is too small, water won’t drain fast enough, and you could have plumbing problems. From kitchen sinks to bathroom basins, make sure you know the correct sink drain pipe size for your sinks. Below, we tell you what size you should have and how to see if your pipes measure up.
What Is the Standard Sink Drain Pipe Size?
Because there isn’t just one size of sink, there isn’t one standard sink drain size. Instead, there are three most-common sizes: 1 ¼ inches, 1 ½ inches, and 2 inches in diameter. A fourth option, 3-inch diameter, is rare in home settings but more common in commercial kitchens. The right size to choose depends on the size and water capacity of your sink and local building codes.
How Does Drain Pipe Size Affect Sinks?
On the surface, it might seem like a drain pipe is a drain pipe, and that most sinks should work with any average-sized pipe. But installing the correct size for each sink is important for efficient drainage and to prevent future plumbing problems, including clogs and reduced drain velocity.
When a sink has an optimally sized drain pipe, water flows down and out of the pipe and into the attached plumbing lines that move it out of your home to the sewer or septic system. On this journey, water flows through the P-trap, where some water remains to block sewage fumes from rising into your home.
If the drain pipe is too small, you will notice that water takes a lot longer to drain. When it doesn’t flow down and out with enough force to move debris, you can be left with slow-draining fixtures and having to figure out how to clear clogs that block pipes and cause backups in sinks, other water-draining appliances, and the rest of your plumbing system. You may also have to pay for regular drain cleaning services.
Drain pipes that are too big have fewer problems, but they’re still not ideal. If the drain pipe is oversized for the sink it’s attached to, solids can settle at the bottom of the pipe, which increases the chances of blockages. Oversized pipes can also keep water from flowing at the right speed, as bigger piping decreases suction down into the sewer pipes. You may also notice stinky pipe and sewer odors in your home if the pipe is large enough that it causes a dry P-trap, or prevents the P-trap from holding onto enough water to block fumes from rising up and out of the pipes.
Local plumbing codes and sink manufacturers recommend the best drain pipe size for specific installations. Follow these recommendations when installing sinks to get the best results and protect your home’s plumbing in the future.
Sink Drain Pipe Size by Type
So, what size pipe is best for your sink drain? Different sinks require different sized drain pipes. That’s because the size of the sink changes the water capacity, and sinks with larger capacities need larger drain pipes to quickly and efficiently drain water.
| Type of Sink | Most Common Drain Pipe Diameter |
|---|---|
| Bathroom Sink | 1 ¼ inches (32 mm) |
| Kitchen Sink | 1 ½ inches (38 mm) |
| Double Sink | 2 inches (50 mm) |
| Commercial Sink | 3 inches (80 mm) |
Bathroom Sink Drain Sizes
The most common drain pipe size recommended for average-sized bathroom sinks is 1 ¼ inch in diameter. Smaller kitchen sinks may also call for this size piping. It’s also the typical size for other small to medium-sized sinks that get light use, or an average of 30 minutes or fewer of use per day.
Kitchen Sink Drain Sizes
The most common kitchen sink drain size is 1 ½ inch. This is also a common size for larger bathroom sinks and other sinks that hold a larger volume of water and need a larger drainage capacity. Sinks that get more than average use may also be good candidates for this mid-range drain pipe size to keep the water flowing.
Double Sink Drain Sizes
The most common double sink drain size is 2 inches. You’ll also see this drain size in utility sinks and other sinks with high water flow requirements. In some cases, plumbers recommend these larger-diameter pipes in conjunction with slightly higher water flow to move waste water out of homes that are a long distance from the main sewer.
Commercial Sink Drain Sizes
Commercial sinks and others that get very heavy use can require 3-inch drainage pipes. These pipes are generally best as parts of complex and heavy-duty drainage systems and are almost never found in homes.
How to Measure the Right Size Sink Drain Pipe
If your sink isn’t draining well and you’ve ruled out problems like clogs, the next step is making sure the drain pipes are big enough. Measuring the size of your existing sink drain pipes is a fairly straightforward process. You’ll just need a few basic tools and the ability to get underneath your sink.
Collect a tape measure or ruler, a pen, and a piece of paper to write on.
Find the drain pipe underneath the sink. It will be located directly under the sink drain, which is often in the center of the basin.
Use the tape measure or ruler to measure the diameter of the pipe (half of the total circumference, or the distance across the widest part of the pipe).
Write down this number and compare it to the recommended sizes (generally 1 ¼ inches, 1 ½ inches, 2 inches, or possibly 3 inches, depending on the size of your sink).
If you struggle to measure the pipe or can’t figure out if it’s the right size for your sink, call a local drain cleaning company or plumber near you.
Factors That Influence Sink Drain Plumbing
There are several factors that help determine how big your sink drain pipes should be. Here are the top influencers:
Sink Size and Type
Your sink type and size play the biggest role in which size drain pipe you need. The bigger the sink, the larger the drain pipe you should install. For example, large sinks that you fill and then drain all at once, like double kitchen sinks and utility sinks, will need larger diameter drain pipes than small bathroom sinks to accommodate the large volume of water.
Fixture Requirements
Manufacturers often print recommended drain pipe sizes on sink packaging. If you’re buying a new sink, pay attention to that number and see if your existing drain pipe meets or exceeds it. If not, you may want to update that pipe when you replace the sink.
Sink Use
The way you use your sink will also let you know which diameter of pipe to choose. For example if you’ve paired your sink with a high-pressure or high-flow faucet or you tend to pour large amounts of water down the sink all at once (think emptying large pots of water or pulling the drain plug on a utility sink filled to the brim), you’ll want a larger drain pipe to deal with all of the water.
Pipe Materials
Pipes can be made of PVC (polyvinyl chloride), ABS (acrylonitrile butadiene styrene), iron, steel, and other materials. Manufacturers and codes can recommend different pipe sizes depending on your pipe material.
Plumbing Specifics
Your home’s plumbing system layout and configuration may require a certain drain pipe size that’s compatible with the rest of the system. This can also be a factor if you connect other appliances to your drain pipe, such as a dishwasher or garbage disposal, with larger pipe recommendations than your sink. Additionally, local building codes can dictate the size of pipe required for your home. You’ll want to discuss these factors with a plumber or other pipe expert to be sure you get it right.
Future Upgrades
You might choose a slightly larger drain pipe if you expect to upgrade your sink to a larger one in the future. This can save you money if you don’t have to upgrade the pipes when you replace your existing sink. However, having a too-large sink drain pipe can increase initial costs, reduce the drain velocity in smaller sinks, and increase the possibility of P-trap malfunction and sewer odors escaping into your home, so don’t go too big. Your plumber should be able to give you advice on sizing.
Budget
The cost of materials, labor, and other parts of the job might dictate the type and size of drain pipes. However, resist the temptation to skimp on quality or choose a downsized drain pipe in an attempt to lower the cost of the job. You likely won’t save all that much, and too-small pipes are likely to cause plumbing problems down the road. In fact, you’ll likely end up paying more in repairs and damages than you might if you installed the right-sized pipe from the start.
What to Do if You Have the Wrong Size Sink Drain Pipe
If your sink drain pipe is the wrong size, you’ll want to fix the problem before plumbing issues catch up with you.
Recheck the measurement. It can be challenging to measure circular pipes, so mistakes are possible. Go ahead and double-check your measurements to confirm that the pipe is too small for the sink capacity.
If you bought a new sink drain pipe that is too small for your current sink, exchange it for a larger, correct size.
If you purchased a new sink that’s too big for your existing drain pipe, consider buying a smaller sink. If you love the new fixture, you can also upgrade your drain pipe to fit the new sink.
Consider buying an adapter or reducer that will allow you to connect pipes of different sizes. You’ll need to buy adapters that are compatible with your plumbing setup and follow local building codes.
Call a pro. Plumbing problems can be a huge hassle, so don’t do anything that might cause problems down the road. Instead, call a plumber or drain expert if you have any questions. It’s better to head off plumbing disasters before issues arise.