In short: a common 3/4-inch pipe (Schedule 40 PVC) holds only about 0.028 US gallons (0.10 L) per foot — roughly a quarter cup. Capacity grows with the square of the diameter, so a 2-inch pipe of the same length holds over six times as much. That water weighs about 8.33 lb per gallon at room temperature — use the calculator above for your exact pipe size and length.
These figures are planning aids based on published pipe dimensions and density data. For code compliance, dosing or structural work, confirm with a licensed plumber or engineer.
How to calculate a pipe's water capacity
A length of pipe is a cylinder, and the water inside it fills that cylinder's interior. Capacity depends on two measurements: the pipe's inside diameter and its length. Because a circle's area grows with the square of its radius, diameter has a far bigger effect on capacity than length does.
This calculator converts your inside diameter and length to meters, applies that formula to get a volume, and converts the result into US gallons, liters, imperial gallons, cubic feet, cubic meters and US quarts. It then multiplies that volume by the density of water at your chosen temperature to report the weight too.
Worked example. Take a 3/4-inch Schedule 40 PVC pipe — actual inside diameter 0.824 in (0.02093 m) — that runs 50 ft (15.24 m). The cross-sectional area is (π ÷ 4) × 0.02093² ≈ 0.000344 m². Multiply by the length: 0.000344 × 15.24 ≈ 0.00524 m³, which is 5.24 liters, or 1.39 US gallons. At 20 °C that water weighs about 11.5 lb (5.23 kg) — the same numbers the calculator shows with those defaults.
Nominal size vs. actual inside diameter. A "1-inch pipe" is a trade name, not a measurement. Pipe walls take up real space, so the true inside diameter is always a bit different from the nominal label — and it varies by material and schedule. Always use the actual inside diameter for accurate capacity, not the size printed on the pipe.
Why diameter matters more than length
Because the formula squares the diameter but only multiplies by length, doubling a pipe's diameter roughly quadruples its water capacity, while doubling its length only doubles it. That's why a short run of wide pipe can hold more water than a long run of narrow pipe — and why choosing the right diameter matters as much for capacity as it does for flow. If you're sizing a pipe from scratch, the Pipe Size Calculator can help you pick a diameter for a target flow rate first.
Length still matters in absolute terms — a longer run always holds more water — but it scales linearly, one-for-one, while diameter's effect compounds. A 200-ft run of 3/4-inch pipe holds about 5.5 gallons; the same length of 1.5-inch pipe holds over 21 gallons, more than four times as much for the same length.
Water capacity by pipe size (Schedule 40 PVC)
Actual inside diameters and capacities for common Schedule 40 PVC sizes — the values this calculator uses for its PVC presets. Nominal size is shown for reference, but the inside diameter is what drives the math.
| Nominal size | Inside diameter | Gallons per foot | Liters per meter |
|---|---|---|---|
| 1/2 in | 0.622 in | 0.0158 | 0.196 |
| 3/4 in (default) | 0.824 in | 0.0277 | 0.344 |
| 1 in | 1.049 in | 0.0449 | 0.558 |
| 1 1/4 in | 1.380 in | 0.0777 | 0.965 |
| 1 1/2 in | 1.610 in | 0.1058 | 1.313 |
| 2 in | 2.067 in | 0.1743 | 2.165 |
| 3 in | 3.068 in | 0.3840 | 4.769 |
| 4 in | 4.026 in | 0.6613 | 8.213 |
Quick reference: copper pipe (Type L)
Copper walls are thinner than PVC's, so a copper pipe of the same nominal size holds a little more water than PVC of the same nominal size — but slightly less than the same nominal size in some other schedules. Use the actual inside diameter when precision matters.
| Nominal size | Inside diameter | Gallons per foot | Liters per meter |
|---|---|---|---|
| 1/2 in | 0.545 in | 0.0121 | 0.151 |
| 3/4 in | 0.785 in | 0.0251 | 0.312 |
| 1 in | 1.025 in | 0.0429 | 0.532 |
| 1 1/4 in | 1.265 in | 0.0653 | 0.811 |
| 1 1/2 in | 1.505 in | 0.0924 | 1.148 |
| 2 in | 1.985 in | 0.1608 | 1.997 |
Worked examples
Winterizing an irrigation main
6.73 gal
150 ft of 1-inch Schedule 40 PVC holds about 6.73 gallons (25.5 L), weighing roughly 56 lb (25.4 kg) — the water you need to blow out or drain before a hard freeze. See the Pipe Fill Time Calculator for how long the reverse — filling it — would take.
Short hot-water supply line
0.48 gal
A 40-ft run of 1/2-inch Type L copper from the water heater to a fixture holds about 0.48 gallons (1.83 L), weighing roughly 4 lb (1.8 kg) — close to what runs down the drain before hot water arrives.
Disinfecting a new water main
87.2 gal
500 ft of 2-inch Schedule 40 PVC holds about 87.2 gallons (330 L), weighing roughly 726 lb (329 kg). Knowing this volume is the first step in calculating a correct chlorine dose for a new-main disinfection flush.
What else affects the result
Pipe schedule and wall thickness. Heavier-duty schedules (like Schedule 80) have thicker walls and a smaller inside diameter than Schedule 40 at the same nominal size, so they hold slightly less water. Always check the actual ID on the manufacturer's spec sheet for critical work.
Fittings and bends. Elbows, tees and valves add a small amount of extra internal volume beyond a straight run, typically well under 5% for a normal residential system. This calculator models straight pipe only; for long runs with many fittings, add a small margin.
Temperature. The pipe's internal volume doesn't change with temperature, but the water's weight does, slightly — see the Water Weight Calculator if you need the exact weight of water across the full 0–100 °C range.
Scale and sediment buildup. Old metal pipe can accumulate mineral scale or corrosion on the inside wall, shrinking the effective inside diameter over years of service. New-pipe dimensions, as used here, won't match an old system exactly.
Frequently asked questions
How much water does a pipe hold per foot?
It depends only on the inside diameter, not the pipe material or pressure rating. A common 3/4-inch Schedule 40 PVC pipe (0.824 in inside diameter) holds about 0.028 US gallons (0.10 L) per foot. A 1-inch pipe holds about 0.045 gal/ft, and a 2-inch pipe holds about 0.174 gal/ft — roughly quadrupling the diameter's effect because capacity scales with diameter squared.
Does pipe wall thickness affect how much water it holds?
Yes. Capacity depends on the inside diameter, and a thicker pipe wall leaves less room for water even when the nominal or outside size is identical. A 3/4-inch Schedule 40 PVC pipe (0.824 in ID) holds noticeably more than a 3/4-inch Type L copper pipe (0.785 in ID) for the same length.
How much does the water in a pipe weigh?
At room temperature (20 °C / 68 °F), one US gallon of water weighs about 8.33 lb (3.78 kg), so multiply the pipe's gallon capacity by 8.33 for pounds. A 3/4-inch pipe, 50 feet long, holds about 1.39 gallons weighing roughly 11.5 lb (5.2 kg).
Why does my pipe hold less water than its nominal size suggests?
Nominal pipe size (like "1 inch") is a trade label, not the actual inside diameter. The pipe wall takes up some of that nominal dimension, so the true inside diameter is always smaller — for 1-inch Schedule 40 PVC it's about 1.049 inches of actual clear bore, and it varies by material and schedule.
Does temperature change how much water a pipe holds?
No — the pipe's internal volume is fixed by its geometry, so the amount of water it holds does not change with temperature. What does change slightly is the weight of that water, because warmer water is a little less dense. The difference between cold and hot tap water is usually under 2%.
Sources & references
- Kell, G. S. (1975). Density, thermal expansivity, and compressibility of liquid water from 0° to 150 °C. Journal of Chemical & Engineering Data, 20(1), 97–105.
- ASTM International. ASTM D1785 — Standard Specification for Poly(Vinyl Chloride) (PVC) Plastic Pipe, Schedules 40, 80, and 120.
- ASTM International. ASTM B88 — Standard Specification for Seamless Copper Water Tube.
John Mac, PE
Water Systems Specialist · Austin, Texas
Texas-licensed Professional Engineer with 13+ years in residential water systems and 180+ completed projects. Writes and reviews the calculators on watercalculator.us. Read full bio
Texas PE (2016) · BS Civil Engineering, Hydraulics (2013)