★ REFERENCE TABLE · CONSTRUCTION · PLUMBING

Copper Pipe Size Chart & Volume Calculator

The number on a copper pipe is not its size — a “3/4-inch” pipe measures 0.875 inches across the outside. The table below gives the real outside diameter, wall thickness, and Type L inside diameter for every common size from 3/8 inch to 2 inches, and the calculator turns any length into gallons: 100 feet of 3/4-inch Type L pipe holds 2.51 gallons of water (2.5142 gallons unrounded). Pick your size and length below to price a run, size a drain-down, or check a fitting.

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How much water does your pipe run hold?

Copper tube sizing is a trade convention, not a measurement: the nominal size is 1/8 inch less than the outside diameter, and the inside diameter then depends on the wall type — K, L, or M — because all three share the same outside diameter so they take the same fittings. Volume follows the inside diameter alone, so two pipes with the same nominal size can hold different amounts of water. This chart pins down Type L, the grade used for most interior plumbing, and the calculator does the cylinder math for any length you enter.

Pipe size (nominal, Type L)

Nominal size. Volume grows with the square of the inside diameter, so a 1-inch pipe holds far more than twice a 1/2-inch pipe.

Length (feet)

Length in feet. Volume is proportional to length: 50 feet of 3/4-inch pipe holds 1.26 gallons, exactly half the 100-foot figure.

Water volume in the pipe2.51 gallons100 feet of 3/4-inch Type L pipe, inside diameter 0.785 in, holds 2.51 gallons (2.5142 gallons unrounded). The same length of 1/2-inch pipe holds 1.21 gallons; 1-inch holds 4.29 gallons; 2-inch holds 16.08 gallons.

100 feet of 3/4-inch Type L pipe holds 2.51 gallons. Volume = π × (inside diameter ÷ 2)² × length ÷ 231 cubic inches per gallon.

Type L copper pipe dimensions

Print this table for the job site: nominal size, actual outside diameter, Type L wall thickness, and Type L inside diameter, all in inches. Outside diameter is fixed across types K, L, and M for a given nominal size — only the wall, and therefore the inside diameter, changes. A note on the 3/8-inch row: the correct Type L inside diameter is 0.430 inches (0.500 outside minus twice the 0.035-inch wall); 0.402 inches is the thicker-walled Type K value for the same size and is not used here.

Nominal size	Outside diameter (in)	Type L wall (in)	Type L inside diameter (in)
3/8 in	0.500	0.035	0.430
1/2 in	0.625	0.040	0.545
3/4 in	0.875	0.045	0.785
1 in	1.125	0.050	1.025
1-1/4 in	1.375	0.055	1.265
1-1/2 in	1.625	0.060	1.505
2 in	2.125	0.070	1.985

The model, stated exactly

Inside diameter = outside diameter − 2 × wall thickness (Type L walls above). Volume in cubic inches = π × (inside diameter ÷ 2)² × length in inches (feet × 12). Gallons = cubic inches ÷ 231. The calculator treats the pipe as a straight, empty cylinder: it does not subtract the volume taken up by fittings, valves, or solder joints, and it does not count water standing in fixtures. For drain-down and fill estimates, add a small allowance for fittings on long runs with many elbows.

The worked example, line by line

Setup: 3/4-inch Type L, inside diameter 0.785 in, length 100 ft.

Line 1 — radius. 0.785 ÷ 2 = 0.3925 in.

Line 2 — cross-section. π × 0.3925² = 0.4839 sq in.

Line 3 — length in inches. 100 × 12 = 1,200 in.

Line 4 — volume. 0.4839 × 1,200 = 580.8 cubic inches.

Line 5 — gallons. 580.8 ÷ 231 = 2.51 gallons (2.5142 unrounded).

Try these

1/2-inch pipe, 100 feet. Inside diameter 0.545 in gives 1.21 gallons — less than half the 3/4-inch figure, because volume follows the square of the diameter.

1-inch pipe, 100 feet. Inside diameter 1.025 in gives 4.29 gallons.

3/4-inch pipe, 50 feet. Half the length gives 1.26 gallons — volume is exactly proportional to length.

2-inch pipe, 100 feet. Inside diameter 1.985 in gives 16.08 gallons — the big main holds more than six times the 3/4-inch branch.

Output · formula · meaning

Output	Formula	What it means
Inside diameter	Outside diameter − 2 × wall	0.785 in for 3/4-inch Type L — the bore the water actually flows through.
Cross-section area	π × (inside diameter ÷ 2)²	0.4839 sq in for 3/4-inch Type L.
Length in inches	Feet × 12	1,200 in for 100 feet.
Volume	Area × length ÷ 231	2.51 gallons for 100 feet of 3/4-inch Type L.

Who uses this

The plumber draining a system before a repair: enters the main's size and length to know whether a bucket or a wet-vac is the right tool before opening a joint.
The homeowner sizing a water-heater drain-down: enters the hot-water run to estimate how much water must come out before the heater can be swapped.
The DIYer buying fittings: checks the chart to confirm a “3/4-inch” fitting really means a 0.875-inch outside diameter, and that Type L and Type M take the same fitting but hold different volumes.
The estimator pricing a re-pipe: uses the chart to match old pipe sizes to new Type L stock and the calculator to total the water standing in long commercial runs.

Accuracy & limitations

Dimensions are the standard CTS (copper tube size) values for Type L drawn or annealed tube; manufacturing tolerance is a few thousandths of an inch, which moves the gallon figure by well under 1% on ordinary runs. The volume figure is for the pipe bore only: elbows, tees, valves, and water-heater tanks are not included, and a run with many fittings holds slightly less water than the straight-pipe figure. Refrigeration (ACR) copper uses different sizing — its nominal size is the outside diameter — so do not use this chart for air-conditioning lines. Error policy: a missing or non-positive length, or an unrecognized size, is reported as an error rather than calculated.

Cite this calculatorBright Side Kit. “Copper Pipe Size Chart & Volume Calculator — Bright Side Kit.” brightoolbox.com, 2026.

Bright Side Kit. "Copper Pipe Size Chart & Volume Calculator." https://brightoolbox.com/copper-pipe-size-chart/ Accessed October 24, 2026.

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Frequently asked questions

What is the actual outside diameter of 3/4-inch copper pipe?

0.875 inches. Copper tube nominal sizes run 1/8 inch below the outside diameter, so 3/4-inch pipe measures 7/8 inch outside, 1/2-inch measures 5/8 inch, and 1-inch measures 1-1/8 inches.

What is the inside diameter of 3/4-inch Type L copper pipe?

0.785 inches. The 0.875-inch outside diameter minus twice the 0.045-inch Type L wall leaves a 0.785-inch bore. Type K of the same size is 0.745 inches and Type M is 0.811 inches, because the wall differs.

How much water does 100 feet of 3/4-inch copper pipe hold?

2.51 gallons. The bore area of 0.4839 square inches times 1,200 inches of length is 580.7 cubic inches, and 231 cubic inches make a gallon.

What is the difference between Type K, L, and M copper pipe?

Wall thickness only. Type K is thickest (for underground and high-pressure work), Type L is the middle grade used for most interior plumbing, and Type M is thinnest (for low-pressure and drainage work where code allows). All three share the same outside diameter and take the same fittings.

Why is the nominal size smaller than the actual pipe?

It is a historical trade convention. The nominal size once approximated the inside diameter of early pipe, but as walls standardized, the outside diameter became the fixed dimension for fittings while the nominal label stayed behind by 1/8 inch.

Does Type L hold more water than Type K?

Yes, slightly: the thinner Type L wall leaves a wider bore. For 3/4-inch pipe, Type L holds 2.51 gallons per 100 feet against about 2.27 gallons for Type K (0.745-inch bore). The difference is small on short runs and worth counting on long ones.

Can I use this chart for refrigeration copper lines?

No. Refrigeration (ACR) copper is sized by its outside diameter, not by the plumbing nominal convention, so a 3/4-inch ACR tube measures 0.750 inches outside. Use an ACR chart for air-conditioning and refrigeration work.

Do fittings change the volume?

Slightly. Elbows, tees, and valves displace a small amount of water, so a run with many fittings holds a little less than the straight-pipe figure here. For drain-down estimates, treat this figure as a close upper bound.