Pipe Size Chart

Standard Pipe Size Chart

Nominal pipe size is a category name rather than a physical measurement. Steel, Schedule 40 PVC, and Schedule 80 PVC pipe follow the iron-pipe-size standard, which keeps the outside diameter identical across all schedules for a given nominal size.

The dimensional standards governing these figures are ASME B36.10M for wrought steel pipe and ASTM D1785 for Schedule 40 and Schedule 80 PVC pipe. Copper water tube dimensions follow ASTM B88 and are described by the Copper Development Association. The table below lists the standard nominal sizes alongside their outside diameters, Schedule 40 wall dimensions, metric DN equivalents, and copper outside diameters.

Nominal Pipe Size and Wall Schedule

Nominal pipe size designates the fitting family rather than a measurable dimension. Because the outside diameter of iron-pipe-size pipe is fixed, any change in wall thickness alters the interior channel rather than the exterior profile.

The schedule rating defines the wall thickness of the pipe. A higher schedule number indicates a thicker pipe wall, which reduces the inside diameter while preserving the standard outside diameter so fittings can join the exterior surface.

Inside diameters listed for Schedule 40 PVC are approximate values calculated by subtracting two wall thicknesses from the outside diameter. Manufacturing tolerances create minor variations in the actual interior dimension, so users should check the product's printed markings on the pipe wall.

Differences Between Copper, PEX, and PVC Sizing

Copper water tube uses copper tube size dimensions, which do not match iron-pipe-size dimensions. The outside diameter of Types K, L, and M copper tube is exactly 1/8 inch larger than its nominal designation.

Because of this difference, a 1/2-inch copper tube has an outside diameter of 0.625 inches, whereas a 1/2-inch PVC pipe has an outside diameter of 0.840 inches. These two materials cannot share slip-on fittings, and their nominal labels cannot be interchanged by visual estimation.

Cross-linked polyethylene (PEX) tubing follows copper tube size outside diameter standards under ASTM F876. Nominal 1/2-inch PEX tubing measures approximately 0.625 inches on the outside, matching the dimension of copper water tube fittings. Joining PEX tubing to iron-pipe-size threaded fittings requires dedicated transitional adapters.

Schedule 40 and Schedule 80 CPVC follow iron-pipe-size dimensions, but residential hot-and-cold CPVC water tubing commonly uses copper tube size dimensions. Check the printed text on the tubing wall to confirm whether it is iron pipe size or copper tube size before selecting fittings. To review how plastic plumbing materials compare in service, see our guide on PVC vs CPVC pipe.

How to Determine Pipe Size on Existing Lines

Determining the size of an existing pipe requires finding its outside diameter rather than attempting to reach inside the line. You can determine the outside diameter by taking a direct measurement or by calculating it from the pipe's circumference.

Use calipers to measure across the widest exterior cross-section of the pipe. If you are learning the tool, refer to our tutorial on how to read a caliper. If you do not have calipers, wrap a flexible string or strip of paper around the pipe barrel, mark the point of overlap, measure the resulting length to obtain the circumference, and divide that number by 3.14 to find the outside diameter.

Match your calculated outside diameter against the table to locate the nominal size. Remember to confirm whether the line is copper or plastic, because an outside diameter near 0.875 inches indicates 3/4-inch copper tube, whereas an outside diameter of 0.840 inches indicates 1/2-inch iron-pipe-size pipe. When access allows, read the printed text stamped along the pipe barrel, which lists the nominal size, material type, schedule, and ASTM specification.

National Pipe Taper Threads and Hose Threads

Threaded plumbing fittings use National Pipe Taper threads, which incorporate a slight taper along the threaded profile. The taper allows mating threads to wedge together to form a mechanical seal when tightened with thread sealant or tape.

Tapered pipe threads are designated by the nominal size of the pipe rather than the physical diameter of the thread crests. A 3/4-inch National Pipe Taper fitting threads directly onto a pipe with a nominal size of 3/4 inch and an outside diameter of 1.050 inches.

Tapered pipe threads are not compatible with straight hose threads. Garden hose threads use a straight profile designed to seal against an internal rubber washer rather than through thread engagement, and attempting to thread a hose fitting onto a National Pipe Taper fitting prevents a proper seal.

Residential Water Supply and Drain Sizes

In typical residential water supply practice, plumbers run a 3/4-inch or 1-inch main supply pipe from the water meter or well pressure tank into the home, then branch off with 1/2-inch lines to individual fixtures. This configuration represents common practice rather than a universal requirement.

Actual water supply sizing depends on the total fixture count, required flow rates, available water pressure, total pipe length, and local plumbing regulations. Calculating supply pipe sizing requires a licensed plumbing contractor.

Drain, waste, and vent systems rely on gravity drainage and specify minimum pipe diameters based on fixture discharge loads. Typical minimum drain or trap sizes under model plumbing codes include about 1-1/4 inches for bathroom sinks, about 1-1/2 inches for kitchen sinks and bathtubs, about 2 inches for clothes washer standpipes, and about 3 inches for toilet drains, which usually connect into a 3-inch or 4-inch branch.

Model plumbing codes include the International Plumbing Code published by the International Code Council and the Uniform Plumbing Code published by the International Association of Plumbing and Mechanical Officials. Local jurisdictions adopt and amend these codes individually. For drainage layout considerations, read our guide on P-trap vs S-trap configurations, or compare drainage plastics in PVC vs ABS pipe.

Fuel Gas Piping Sizing

No gas pipe size chart or gas line diameters appear here. Sizing gas piping requires calculating the total British Thermal Unit demand of all connected appliances, measuring the length of the longest run from the supply meter or regulator, and determining the gas type and delivery pressure.

Gas pipe sizing tables are defined in the National Fuel Gas Code, NFPA 54, published by the National Fire Protection Association. Sizing, modifying, assembling, and testing fuel gas systems is work for a licensed plumber or gas fitter. An undersized or leaking fuel line presents severe fire, explosion, and carbon monoxide hazards.

Metric DN Equivalents and Excluded Systems

Metric systems designate pipe using diameter nominal ratings, abbreviated as DN. Like nominal pipe size, a DN rating is a standardized category name rather than a precise metric measurement.

Under this classification, DN 15 corresponds to 1/2-inch pipe, DN 20 corresponds to 3/4-inch pipe, DN 25 corresponds to 1-inch pipe, DN 32 corresponds to 1-1/4-inch pipe, DN 40 corresponds to 1-1/2-inch pipe, DN 50 corresponds to 2-inch pipe, DN 80 corresponds to 3-inch pipe, DN 100 corresponds to 4-inch pipe, and DN 150 corresponds to 6-inch pipe.

This chart applies strictly to United States plumbing standards. Industrial and commercial chilled-water piping, electric resistance welded pipe, high-density polyethylene mill charts, and foreign sizing standards used in the United Kingdom, Australia, or India fall outside the scope of this reference and are not interchangeable with these dimensions.

Common questions

What size is 3/4-inch pipe?

A 3/4-inch iron-pipe-size pipe has an outside diameter of 1.050 inches, while a 3/4-inch copper tube has an outside diameter of 0.875 inches. Neither material measures exactly 0.75 inches across the outside.

How do you measure pipe diameter?

Measure the outside diameter with a caliper across the exterior surface of the pipe. You can also wrap a string around the pipe to measure its circumference, divide that value by 3.14, and compare the result to a pipe size chart.

Is 1/2-inch PVC the same size as 1/2-inch copper?

No, 1/2-inch PVC has an outside diameter of 0.840 inches, while 1/2-inch copper tube has an outside diameter of 0.625 inches. Because copper follows copper tube size standards and PVC follows iron pipe size standards, the materials use different fitting dimensions.

What does Schedule 40 mean?

Schedule 40 indicates a specific wall thickness standard for iron-pipe-size pipe. Higher schedule numbers specify thicker walls, which reduce the inside diameter while keeping the outside diameter constant.

What is DN in pipe sizing?

DN stands for diameter nominal, which is the metric equivalent to nominal pipe size used under international standards. Like nominal pipe size, DN is a designation name rather than a direct millimeter measurement.

What size pipe is used for a toilet drain?

Typical minimum drain sizes under model plumbing codes specify about 3 inches for a toilet drain, which usually discharges into a 3-inch or 4-inch building drain branch. Local code requirements govern the final installation.

What size pipe do I need for a gas line?

Gas line sizing cannot be determined from a general reference table. Sizing gas piping requires a licensed professional who calculates the total appliance British thermal unit (BTU) demand, run length, pressure, and gas type according to NFPA 54 standards.

Related

• How to Read a Caliper
• PVC vs CPVC
• P-Trap vs S-Trap
• PVC vs ABS