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Piping
How to Measure Pipe Size Download Article Co-authored by David Balkan
Last Updated: March 10, 2025 Fact Checked
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Measuring the Right Diameter
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Converting to Nominal Pipe Size
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This article was co-authored by David Balkan. David Balkan is a Professional Plumber, CEO of Balkan Sewer and Water Main Service, and President of Balkan Sewer and Drain Cleaning. As a hands-on owner of these companies for over 40 years, David is knowledgeable about water service lines, sewers, and drain line issues. David is a Committee Chairman of the Master Plumbers Council and has sat on the Executive Committee of the Sub Surface Plumbers Association of New York for over 30 years. His knowledge and solution-oriented approach contributed to Balkan Sewer and Water Main Service being the largest and most trusted service in New York City and the recipient of the 2017 Angie’s List Super Service Award. This article has been fact-checked, ensuring the accuracy of any cited facts and confirming the authority of its sources. This article has been viewed 430,164 times.
Measuring pipe size can be a little confusing at first, but anyone can learn how to do it. To find the right size, first figure out if you need to measure the outside or inside diameter, then measure it with a ruler or tape measure. Then you’ll need to convert the measurement to the “nominal” pipe size, or what that pipe will be called in the store. Measuring pipe size is an important skill to have under your belt for your plumbing and building projects.
How do you measure pipe diameter?
To find it, measure around the circumference of the pipe with flexible measuring tape. Divide the circumference by pi, or about 3.14159. For example, if the circumference is 12.57 inches (319 mm), you would divide by pi, and get an outside diameter of about 4 inches (100 mm).
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Part 1 Part 1 of 2:
Measuring the Right Diameter
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1 Determine if your pipe has “male” or “female” threads or no threads. Threads are the little grooves on the ends of some pipes that help them fit together. Male threads are on the outside of the pipe, whereas female threads are on the inside.[1]XResearch source
2 Find the outside diameter if the pipe has male threads or no threads. The outside diameter is from outside edge to outside edge across the pipe. To find it, measure around the circumference of the pipe with flexible measuring tape. Divide the circumference by pi, or about 3.14159.
For example, if the circumference is 12.57 inches (319 mm), you would divide by pi, and get an outside diameter of about 4 inches (100 mm).
Use string to measure if you don’t have measuring tape. Mark the point on the string where it wraps around the circumference. Then remove the string, measure it against a ruler, and divide that length by pi.
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3 Measure the inside diameter if the pipe has female threads. That is the distance across the middle of the pipe, not including the thickness of the pipe walls. Use a ruler or a caliper and measure at the end of the pipe, where there is a cross section.[2]XResearch source [3]X Expert Source David BalkanProfessional Plumber & CEO of Balkan Sewer & Water MainExpert Interview
Remember not to measure from the outside edges, but rather from inside edge to inside edge.
EXPERT TIP
Greg Jeiranyan
Licensed Plumber Greg Jeiranyan is a Licensed Plumber based in Los Angeles, California. With over 10 years of professional experience, Greg and his team specialize in residential and commercial plumbing service calls. His company, Plumbing Geeks, is rated 5 stars on Yelp and is a family-owned and operated plumbing company. Plumbing Geeks has been serving Los Angeles and its surrounding areas since 2021. Greg Jeiranyan Licensed Plumber
Use a tape measure across the pipe's width to determine the size. A simple way to measure a pipe's diameter is to use a tape measure across the width of the pipe. This gives you the size quickly without specialized tools. It's very handy for replacements or repairs. This easy method works great for professionals and DIYers.
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Converting to Nominal Pipe Size
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1 Convert your diameter to nominal size if its smaller than 14 inches (360 mm). If its 14 inches (360 mm) or more, you don’t need to convert it, because the diameter will equal the nominal diameter already.[4]XResearch source
2 Find out if you need to convert to NPS or DN. Convert to Nominal Pipe Size (NPS) if you are in North America, or Diameter Nominal (DN) if you are using the metric system.
If you are unsure, it could help to go to the website of a store in your country that sells pipe. If they mark pipe with inches, then you need the NPS system.
3 Convert your measurement of internal or outside diameter to the appropriate nominal size. Nominal size is what the pipe will be called in the store. You can do this using a table. [5]XResearch source
This table is helpful for NPS measurements: https://blog.enerpac.com/wp-content/uploads/2020/10/NPS-nominal-pipe-size-chart-inches.pdf
This table has both NPS and DN measurements: https://www.massflow-online.com/faqs/where-do-nps-or-dn-stand-for/
For example, if you measured a diameter of 1.05 inches (27 mm), this would translate to a nominal size of ¾ in NPS, or 20 in DN.
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Expert Q&A
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Question How do I know what size copper pipe I have? David Balkan Professional Plumber David Balkan is a Professional Plumber, CEO of Balkan Sewer and Water Main Service, and President of Balkan Sewer and Drain Cleaning. As a hands-on owner of these companies for over 40 years, David is knowledgeable about water service lines, sewers, and drain line issues. David is a Committee Chairman of the Master Plumbers Council and has sat on the Executive Committee of the Sub Surface Plumbers Association of New York for over 30 years. His knowledge and solution-oriented approach contributed to Balkan Sewer and Water Main Service being the largest and most trusted service in New York City and the recipient of the 2017 Angie’s List Super Service Award. David Balkan Professional Plumber Expert Answer Measure the outer diameter of your pipe with a caliper. Then, check online for a pipe sizing chart. Compare the caliper measurement you collected with the sizing chart, and you'll know exactly which size you're working with. Thanks! We're glad this was helpful.Thank you for your feedback. If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even $1 helps us in our mission. Support wikiHow Yes No Not Helpful 11 Helpful 22
Question What are standard pipe sizes? David Balkan Professional Plumber David Balkan is a Professional Plumber, CEO of Balkan Sewer and Water Main Service, and President of Balkan Sewer and Drain Cleaning. As a hands-on owner of these companies for over 40 years, David is knowledgeable about water service lines, sewers, and drain line issues. David is a Committee Chairman of the Master Plumbers Council and has sat on the Executive Committee of the Sub Surface Plumbers Association of New York for over 30 years. His knowledge and solution-oriented approach contributed to Balkan Sewer and Water Main Service being the largest and most trusted service in New York City and the recipient of the 2017 Angie’s List Super Service Award. David Balkan Professional Plumber Expert Answer It depends on the type of pipe you're working with. Search online for a pipe sizing chart, which can point you in the right direction. Thanks! We're glad this was helpful.Thank you for your feedback. If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even $1 helps us in our mission. Support wikiHow Yes No Not Helpful 11 Helpful 9
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Tips
If you have tubing, instead of piping, you don’t need to convert to nominal diameter. Tubing is named based on the outside diameter. Thanks Helpful 2 Not Helpful 3
Tables can also help you find out the “schedule” of your pipe, which is related to the wall thickness. Thanks Helpful 1 Not Helpful 2
If you have PEX, Cross-Linked Polyethylene Tubing, the nominal diameter is equivalent to the internal diameter. Thanks Helpful 0 Not Helpful 0
Submit a Tip All tip submissions are carefully reviewed before being published Name Please provide your name and last initial Submit Thanks for submitting a tip for review! Advertisement
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References
↑ https://www.youtube.com/watch?v=0siJQV5TGhc
↑ https://www.youtube.com/watch?v=ifPkWJuBJoM
↑ David Balkan. Professional Plumber & CEO of Balkan Sewer & Water Main. Expert Interview
Co-authored by: David Balkan Professional Plumber This article was co-authored by David Balkan. David Balkan is a Professional Plumber, CEO of Balkan Sewer and Water Main Service, and President of Balkan Sewer and Drain Cleaning. As a hands-on owner of these companies for over 40 years, David is knowledgeable about water service lines, sewers, and drain line issues. David is a Committee Chairman of the Master Plumbers Council and has sat on the Executive Committee of the Sub Surface Plumbers Association of New York for over 30 years. His knowledge and solution-oriented approach contributed to Balkan Sewer and Water Main Service being the largest and most trusted service in New York City and the recipient of the 2017 Angie’s List Super Service Award. This article has been viewed 430,164 times. 70 votes - 83% Co-authors: 8Updated: March 10, 2025 Views: 430,164 Categories: Piping In other languages Dutch Hindi Czech Japanese
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Jennifer M.
Aug 1, 2024
"I needed to find the outer diameter of an inground, broken pipe. This information helped me immediately. I was able to make my repair for a high school baseball field within minutes."..." more
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Yes No Advertisement Cookies make wikiHow better. By continuing to use our site, you agree to our cookie policy. Co-authored by: David Balkan Professional Plumber Co-authors: 8Updated: March 10, 2025 Views: 430,16483% of readers found this article helpful. 70 votes - 83% Click a star to add your vote 83% of people told us that this article helped them.
Jennifer M.
Aug 1, 2024
"I needed to find the outer diameter of an inground, broken pipe. This information helped me immediately. I was able to make my repair for a high school baseball field within minutes."..." more Share yours!
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Co-authored by: David Balkan Professional Plumber This article was co-authored by David Balkan. David Balkan is a Professional Plumber, CEO of Balkan Sewer and Water Main Service, and President of Balkan Sewer and Drain Cleaning. As a hands-on owner of these companies for over 40 years, David is knowledgeable about water service lines, sewers, and drain line issues. David is a Committee Chairman of the Master Plumbers Council and has sat on the Executive Committee of the Sub Surface Plumbers Association of New York for over 30 years. His knowledge and solution-oriented approach contributed to Balkan Sewer and Water Main Service being the largest and most trusted service in New York City and the recipient of the 2017 Angie’s List Super Service Award. This article has been viewed 430,164 times. 70 votes - 83% Co-authors: 8 Updated: March 10, 2025 Views: 430,164 Categories: Piping In other languages Dutch Hindi Czech Japanese 
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1 Determine if your pipe has “male” or “female” threads or no threads. Threads are the little grooves on the ends of some pipes that help them fit together. Male threads are on the outside of the pipe, whereas female threads are on the inside.[1] 
2 Find the outside diameter if the pipe has male threads or no threads. The outside diameter is from outside edge to outside edge across the pipe. To find it, measure around the circumference of the pipe with flexible measuring tape. Divide the circumference by pi, or about 3.14159. 
3 Measure the inside diameter if the pipe has female threads. That is the distance across the middle of the pipe, not including the thickness of the pipe walls. Use a ruler or a caliper and measure at the end of the pipe, where there is a cross section.[2] [3] 
1 Convert your diameter to nominal size if its smaller than 14 inches (360 mm). If its 14 inches (360 mm) or more, you don’t need to convert it, because the diameter will equal the nominal diameter already.[4] 
2 Find out if you need to convert to NPS or DN. Convert to Nominal Pipe Size (NPS) if you are in North America, or Diameter Nominal (DN) if you are using the metric system. 
3 Convert your measurement of internal or outside diameter to the appropriate nominal size. Nominal size is what the pipe will be called in the store. You can do this using a table. [5] 
David Balkan Professional Plumber David Balkan is a Professional Plumber, CEO of Balkan Sewer and Water Main Service, and President of Balkan Sewer and Drain Cleaning. As a hands-on owner of these companies for over 40 years, David is knowledgeable about water service lines, sewers, and drain line issues. David is a Committee Chairman of the Master Plumbers Council and has sat on the Executive Committee of the Sub Surface Plumbers Association of New York for over 30 years. His knowledge and solution-oriented approach contributed to Balkan Sewer and Water Main Service being the largest and most trusted service in New York City and the recipient of the 2017 Angie’s List Super Service Award. 
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