A P trap is a curved pipe installed below sinks and other plumbing fixtures to hold water and prevent sewer gas from entering buildings. For kitchen sinks, the most common P trap size is 1.5 inches in diameter. This standard size is suitable for most residential kitchen sink drains and provides adequate water flow while still trapping gases effectively.
What size P trap for kitchen sink? As a commonly asked question when installing or replacing a kitchen sink, the answer is typically 1.5 inches. This fits most standard residential kitchen sink piping and maintains proper drainage and venting according to plumbing codes. Using the correct P trap size is important to prevent clogs or slow drainage over time.
While 1.5 inches is the normal P trap diameter for a kitchen sink, the size can vary depending on the specifics of your plumbing system. The drain pipe size, existing trap configuration, and sink basin volume may require a different P trap size to ensure proper water flow and trap seal depth. Considering these factors will determine what size P trap for kitchen sink is best.
What Size P Trap Is Needed For A Kitchen Sink?
The standard size P trap for a kitchen sink is 1-1/2 inches inside diameter. This is the typical size used to connect kitchen sink drains to the drain pipes in the wall or floor. When replacing an existing kitchen sink P trap, Size P Trap For Kitchen Sink it is best to use the same size as the original to ensure proper fit with the other pipes and connections. Using a P trap that is too small or too large will not allow a secure connection.
The Standard P Trap Sizes For Kitchen Sinks
As mentioned above, the standard kitchen sink P trap size is 1-1/2 inches inside diameter. This size is used for most residential kitchen sinks with a single or double basin. The 1-1/2 inch size provides adequate drainage capacity for typical household use while still fitting properly under most kitchen sinks.
Smaller P traps, such as 1-1/4 inches, are generally only used for bathroom sink drains which require lower drainage capacity. Larger sizes may be needed for some commercial kitchen sinks.
Measure To Find The Right Size P Trap For My Kitchen Sink
First, check under the kitchen sink to identify the existing P trap size by measuring the inside diameter of the u-shaped bend, which should be marked. If no P trap is currently installed, measure the diameter of the drain tailpiece that extends from the sink.
This should match the required P trap size. Also measure the distance between the tailpiece and the drain pipe in the wall to determine the total P trap length needed. Getting accurate measurements before purchasing ensures getting the correctly sized P trap kit.
Factors Determine The Best P Trap Size For A Kitchen Sink
The size of the drain pipe under the sink determines P trap size. Standard is 1 1/2 inch pipe, needs 1 1/2 inch P trap.
Distance to main pipe matters. Long distances may need wider 2 inch pipe and P trap.
More fixtures on shared pipe require wider P traps. Accommodates more water flow.
Check local plumbing codes for legal requirements on sizes. Follow regulations.
Bigger P traps hold more water to block gases. But small traps less likely to dry out with little use.
Consider space under cabinet. Smaller P trap takes less room. Easier to fit and remove to clean.
Here is a summary in table form:
| Factor | Impact on Best P Trap Size |
| Drain pipe diameter | Standard 1 1/2″ pipe needs 1 1/2″ P trap |
| Distance to main drain pipe | Long distances may require wider 2″ P trap |
| Number of fixtures on drain line | More fixtures need wider P trap |
| Local plumbing codes | Sizes dictated by plumbing regulations |
| Water seal capability | Bigger traps block gases better |
| Space under cabinet | Smaller traps take less room |
Alternative P Trap Size For My Kitchen Sink
Alternative sizes may be needed if there are space limitations under the sink cabinet, if connecting to non-standard drain pipe sizes, or if required by local plumbing codes.
For example, a 1-1/4 inch P trap could work for a small secondary prep or bar sink with lower usage. Or a 2 inch P trap may be specified for oversized commercial sinks. Always check measurements and existing hardware before deciding on a non-standard P trap size for a kitchen sink application.
Size Of My Kitchen Sink Drain Affect The P Trap Size
The size of the kitchen sink drain tailpiece determines the appropriate P trap size. The tailpiece and P trap should have similar diameters to allow proper water flow and prevent clogs.
Using a P trap that is much larger than the tailpiece can slow water flow, allowing debris to accumulate. Conversely, using a P trap that is too small can restrict flow and cause backups. In general, it is best to match the P trap size to the tailpiece diameter.
Kitchen Sink Drain Sizes Are Common That Affect P Trap Sizes
The most common kitchen sink drain and tailpiece sizes are 1 1/4″ and 1 1/2″. 1 1/4″ is typical for smaller or single bowl sinks. 1 1/2″ is common for larger double bowl sinks or sinks with a garbage disposal which requires more flow capacity.
For these tailpiece sizes, the corresponding P trap sizes would be 1 1/4″ and 1 1/2″. Using a 1 1/4″ P trap with a 1 1/2″ tailpiece or vice versa would create a size mismatch and potential drainage problems.
Small Kitchen Sink Drain, What P Trap Size Should I Use
For a smaller single bowl kitchen sink with a 1 1/4″ drain tailpiece, the matching P trap size should be 1 1/4″. This size provides adequate flow while preventing debris accumulation that a larger 2″ P trap may allow.
Some single bowl sinks may have 1 1/2″ drains, in which case a 1 1/2″ P trap would be appropriate. But in general for smaller kitchen sinks, a 1 1/4″ P trap matches well and helps prevent clogs.
Larger Kitchen Sink Drain, What P Trap Size Is Recommended
For larger double bowl sinks or sinks with a garbage disposal, a 1 1/2″ drain tailpiece and 1 1/2″ P trap is typically recommended. The slightly wider diameter allows the additional flow capacity needed for these larger sink configurations.
Jumping up to a 2″ P trap on a 1 1/2″ tailpiece usually causes more problems than it solves. So for most larger kitchen sink drains, a matching 1 1/2″ P trap is the right size choice.
Non-Standard P Trap Size For My Kitchen Sink
Non-standard P trap sizes may be needed if the existing plumbing has an uncommon tailpiece diameter not typical of most sink drains. For example, older homes sometimes have 1 1/2″ drain pipes with a 2″ P trap. Replacing the P trap with a 1 1/2″ size would require repiping the drain as well.
In cases where repiping is not feasible, an adapter fitting can sometimes connect a 1 1/2″ tailpiece to a 2″ P trap. Non-standard trap sizes may also be needed to meet specific building code requirements. Consulting a professional plumber is advisable when dealing with non-standard drain sizes.
Pros And Cons Of Different P Trap Sizes For Kitchen Sinks
The most common P trap sizes used under kitchen sinks are 1.5″ and 2″. The 1.5″ P trap takes up less space but has a smaller waterway which can lead to clogs from food waste.
The 2″ P trap has a wider waterway allowing more waste to pass through, but takes up more space under the sink. Ultimately the choice comes down to available space under the cabinet and personal preference. Those who generate more food waste may opt for the 2″ to prevent clogs.
Benefits Of A Smaller P Trap Under A Kitchen Sink
5 benefits of a smaller 1.5″ P trap under a kitchen sink:
- Takes up less space under the cabinet for more storage.
- Easier to install in tight areas.
- Requires fewer fittings and smaller pipes.
- Weighs less so it’s simpler to remove for cleaning.
- Costs less than a larger P trap.
Issues Might Arise From Using Too Small Of A P Trap For A Kitchen Sink
Using a P trap smaller than 1.5″ for a kitchen sink greatly increases the chance of clogs and backups. Food particles will easily get lodged and accumulate. In addition, an undersized P trap may not provide an adequate water barrier to prevent sewer gasses from entering the home.
This poses health hazards from methane, hydrogen sulfide and other toxic gasses. An overtaxed, undersized P trap is also more likely to leak and cause water damage under the sink over time.
Advantages Does A Larger P Trap Offer For Kitchen Sink Drainage
The most common larger alternative is a 2″ P trap. The wider waterway allows more food waste and particles to easily pass through the system. This significantly decreases the chances of clogging or backups.
In addition, the larger volume of water helps provide a more robust barrier against sewer gas infiltration. The 2″ P trap offers more capacity for high use kitchen sinks.
Potential Problems Can Using Too Large Of A P Trap Cause Under A Kitchen Sink
While less common, using a P trap over 2″ under a typical kitchen sink is generally overkill. An extra-large P trap takes up valuable space under the cabinet for storage. It also requires the use of larger pipes and fittings which can increase costs and complexity of the job.
If the sink use is light, a larger P trap may not retain enough water to keep an adequate gas trap seal, allowing odors to leak into the home. Proper P trap sizing for the application is key.
Install The Properly Sized P Trap For My Kitchen Sink
Kitchen sinks commonly use a 1-1/2″ P trap1. First determine if you need to replace just the P trap or other components like the tailpiece. Measure to find the correct length or orient the existing assembly to determine sizing.
The P trap kit should come with washers, slip nuts, and pipe lubricant for easy assembly. Connect the tailpiece to the sink strainer, adding a T-fitting if needed for a double basin. Attach the trap arm to the drain stub-out, then connect the trap bend. Tighten all joints securely with pliers.
Steps Should I Take To Prepare For Installing A P Trap On A Kitchen Sink
Before installation, turn off the water supply and drain the pipes1. Remove existing pipes from top down, using pliers if necessary. Have a bucket ready to catch water. Ensure you have gathered all the correct parts and tools. Clear space under the sink to work. Check fittings alignment before permanently joining parts. Finally, confirm proper P trap depth and test for leaks once installed.
Equipment And Tools Will I Need To Install The P Trap
You’ll need the appropriately sized P trap kit, likely 1-1/2″ for a kitchen sink. The kit should include washers, slip nuts, pipe lubricant and fittings like a tailpiece, trap arm, and bend. Have adjustable pliers, bucket, towels and flashlight. For double basin sinks, you may need a T-fitting and extra tailpiece. Ensure you have equipment to cut pipes if needed.
P Trap To The Sink Tailpiece And Drain Pipes
First connect the tailpiece to the sink strainer using a washer and slip nut. For double sinks, attach a T-fitting to join tailpieces. Apply lubricant to washers before connecting fittings.
Attach the trap arm to the drain stub-out, keeping the beveled side of washers facing up. Then connect the trap bend to the trap arm in the same orientation. Use pliers to tighten all joints securely without overtightening.
Mistakes Should I Avoid When Installing A P Trap On A Kitchen Sink Drain
Avoid using Teflon tape on slip joints. Prevent leaks by aligning fittings properly without overtightening. Confirm adequate trap seal depth between 2-4 inches. Don’t lower the drain entrance too much as this can cause improper slope.
Inspect for leaks and verify proper drainage flow after installing. Finally, avoid creating an S-trap configuration by ensuring the trap arm connects to the vent system.
Codes And Standards Say About P Trap Sizing For Kitchen Sinks
Plumbing codes generally require that kitchen sink P traps must be at least 1.25 inches in diameter, with larger sizes allowed as needed to match the drain size. For example, the 2018 International Plumbing Code states traps must not be smaller than the waste pipe they connect to.
Common sizes are 1.5 inches or 2 inches. The key aspects for code compliance are maintaining at least a 2 inch water seal while allowing proper drainage flow. Custom P traps meeting these criteria can be used.
Plumbing Codes Cover P Trap Installation Under A Kitchen Sink
At the national level, the International Plumbing Code contains specifications for kitchen sink P traps regarding sizing, connections, sealing, and configuration. More strict local plumbing codes may also apply to kitchen sink drain installations and should be checked.
Typical requirements cover allowable materials, trap arm lengths, proper venting, and access for cleaning and maintenance. Permits and inspections may be needed to verify compliance.
The Code Requirements For P Trap Sizes In Kitchen Sink Drains
The 2018 International Plumbing Code sets a minimum 1.25 inch diameter for sink P traps, with larger diameters allowed as needed to match the connected drain pipe size. Traps must maintain a liquid seal of 2 to 4 inches during use.
Maximum horizontal and vertical distances from the sink drain are set, such as having no more than a 24 inch tailpiece drop. Compliant P traps must also meet standards for materials, sealing, inspection access, and configuration.
Find Information On P Trap Standards For Kitchen Sinks
Details on P trap standards for kitchen sinks can be found in plumbing codes like the International Plumbing Code, which is often adopted locally.
Manufacturers also publish dimensional and performance standards for their products to show compliance. Researching product listings, code manuals, and permit guidelines provides the most reliable P trap requirements for a given kitchen sink install.
Frequently Asked Question
What Is The Standard P Trap Size For A Kitchen Sink Drain?
The most common kitchen sink P trap size is 1-1/2 inches.
Should I Use A 1-1/4 Inch Or 1-1/2 Inch P Trap For My Kitchen Sink?
A 1-1/2 inch P trap is recommended for a standard single or double basin kitchen sink.
What Length Of Tailpiece Do I Need For Connecting A Kitchen Sink P Trap?
The tailpiece length should be between 6 to 8 inches to properly connect the kitchen sink strainer to the P trap.
Can I Use A Flexible P Trap Instead Of A Rigid One Under My Kitchen Sink?
Yes, flexible PVC P traps can also be installed under a kitchen sink as long as proper slope and trap seal depth is maintained.
Do I Need Any Special Fittings Or Parts Beyond The Basic P Trap Kit For My Kitchen Sink?
For a double kitchen sink, you may need a T fitting and additional tailpiece to connect both sink drains to the P trap.
Conclusion
The standard size P trap for most kitchen sinks is 1.5 inches in diameter. This matches the typical drain pipe size and allows proper water flow. Bathroom sinks usually require a smaller 1.25 inch P trap. When replacing an existing kitchen sink P trap, use the same size and material already installed if possible for the best fit.
Plumbing codes set requirements for P traps to have at least a 1.25 inch diameter and maintain a liquid seal depth around 2 inches. The exact dimensions can vary based on the sink and installation. The key aspects for code compliance are to size the P trap to match the connected drain pipe, allow adequate water flow, and meet local regulations.