Pipe Volume Calculator

How Much Water Does a Pipe Hold?

A straight pipe is a cylinder. Volume is V = π × r² × L, where r is half the actual inside diameter and L is the pipe length. Convert cubic inches to US gallons by dividing by 231. One inch of inside diameter over 100 feet holds about 4.08 US gallons — not because “1 inch” is a trade size, but because the bore really is 1 inch.

Use this when you need to fill, drain, flush, or treat a line, estimate water sitting in a long run, or check how heavy a full pipe will be. It does not choose a pipe diameter from fixture demand — that belongs on the pipe sizing calculator.

How to Use the Pipe Volume Calculator

1. Choose US/Imperial (inches and feet) or metric (millimeters and meters).
2. Enter the actual inside diameter, pick a standard pipe, or derive ID from outside diameter and wall thickness.
3. Enter the straight pipe length — or switch to Find length and enter a target volume.
4. Read US gallons first, then liters, cubic feet, cubic meters, water weight, gallons per foot, and liters per meter.
5. Open Advanced only if you need multiple pipes, a partial fill, a flow rate, or a custom fluid density.

Pipe Volume Formula

The calculator uses the same cylinder math for every mode.

• General: V = π × r² × L with r = inside diameter ÷ 2
• Inches and feet to US gallons: US gal = π × (ID ÷ 2)² × (length × 12) ÷ 231
• Required length from a target volume: L = 4V ÷ (π × d²) in matching units
• Inside diameter from wall: ID = OD − 2 × wall thickness

231 cubic inches equal 1 US gallon. Results are US gallons, not Imperial gallons (an Imperial gallon is larger, about 1.2 US gallons). Water weight defaults to 8.34 lb per US gallon — a common planning density near 60°F / 15.6°C. That is not a laboratory density table.

Pipe Volume Examples

These examples are the same function the calculator runs. They use actual inside diameter unless the row says “nominal.”

0.75 in ID × 50 ft is about 1.15 US gallons. Treating 0.75 as a 3/4 in trade size without checking the real bore is how people land on a different number.

Gallons Per Foot of Pipe

For a full circular pipe, gallons per foot is about 0.0408 × ID² when ID is the actual inside diameter in inches. That shortcut is the same formula as 100 feet of 1 in ID ≈ 4.08 gallons. Liters per meter comes from the same cylinder in metric units: L/m = π × (ID_mm ÷ 2000)² × 1000.

Common Pipe Volume and Capacity

Standard-pipe mode looks up a published actual ID. A 2 in Schedule 40 steel or PVC listing is 2.067 in inside, so 100 feet holds about 17.43 US gallons — more than a true 2.000 in bore.

Steel and PVC IDs above come from published OD minus twice the listed or minimum wall. Copper Type L/M IDs are ASTM B88 published bores. PEX SDR-9 IDs are computed from ASTM F876 CTS OD and DR 9. Brand sheets can differ by a few thousandths of an inch.

• Steel — Schedule 40: ASME B36.10M / ANSI B36.10 wrought-steel pipe. Inside diameter = published OD − 2 × listed wall.
• Steel — Schedule 80: ASME B36.10M / ANSI B36.10 wrought-steel pipe. Inside diameter = published OD − 2 × listed wall.
• PVC — Schedule 40: ASTM D1785 IPS PVC. Inside diameter = published OD − 2 × minimum wall. Average IDs from a brand sheet can be slightly smaller.
• PVC — Schedule 80: ASTM D1785 IPS PVC. Inside diameter = published OD − 2 × minimum wall. Average IDs from a brand sheet can be slightly smaller.
• Copper — Type L: ASTM B88 drawn copper water tube — published inside diameters for Type L and Type M.
• Copper — Type M: ASTM B88 drawn copper water tube — published inside diameters for Type L and Type M.
• PEX — SDR-9 (CTS): ASTM F876 SDR-9 CTS. Inside diameter = OD − 2 × (OD ÷ 9). Brand IDs can vary slightly.

Inside Diameter vs. Nominal Pipe Size

Nominal pipe size is a name. The water sits in the inside diameter. Schedule 40 and Schedule 80 share a nominal size and outside diameter on IPS steel and PVC, but Schedule 80 has a thicker wall, so the bore is smaller and the volume drops. Copper Type L is thicker than Type M, so Type L holds less than Type M at the same nominal size. PEX is copper-tube-size: a 1/2 in PEX listing is not a 0.500 in hole.

If you only have outside diameter and wall thickness, use OD + wall mode. The calculator shows ID = OD − 2 × wall before it reports volume. If you are ordering PEX footage rather than filling a line, use the PEX pipe calculator.

Common Pipe Volume Mistakes

• Using outside diameter as if it were the bore. OD always overstates capacity.
• Treating a 2 in listing as a 2.000 in hole. Schedule 40 steel/PVC 2 in is 2.067 in ID in the table above.
• Mixing inches with meters, or millimeters with feet, without converting.
• Reporting Imperial gallons. This page uses US gallons (231 in³).
• Forgetting a second identical run. Use pipe count instead of doing the math twice.
• Ignoring fittings and valves. They add a little volume; this model is a straight cylinder.
• Assuming a horizontal drain is full. Fall belongs on the drain slope calculator; liquid-depth mode is the advanced option if you know the water height.
• Using volume to pick a pipe size. Size the line from demand with the pipe sizing calculator, then come back for gallons. Hot-water heater size and peak flow are separate: water heater calculator and hot water flow calculator.

Frequently Asked Questions

How do you calculate pipe volume?

Use V = πr²L with r as half the actual inside diameter. For inches and feet, US gallons = π × (ID ÷ 2)² × (length × 12) ÷ 231. 231 cubic inches equal one US gallon.

What diameter should I use for pipe volume?

The actual inside diameter — the bore the liquid sits in. Nominal size and outside diameter are not substitutes unless you convert them to ID.

Should I use inside diameter or outside diameter?

Inside diameter. Outside diameter includes the wall. If you only know OD and wall thickness, use ID = OD − 2 × wall.

How many gallons are in 100 feet of 1-inch pipe?

If the inside diameter is truly 1 inch, about 4.08 US gallons (15.44 L, about 34 lb of water). A 1 in Schedule 40 steel listing is 1.049 in ID and holds a little more.

How many gallons per foot does a pipe hold?

About 0.0408 × ID² US gallons per foot when ID is the actual inside diameter in inches. A 1 in ID pipe holds about 0.0408 gal/ft; a 2.067 in ID pipe holds about 0.174 gal/ft.

Does pipe schedule affect volume?

Yes. Heavier schedules have thicker walls and a smaller bore at the same nominal size, so they hold less. Standard-pipe mode uses the published ID for the schedule you pick.

Can I calculate pipe volume in liters?

Yes. Every result includes liters. Switch to metric to enter millimeters and meters, or stay in US units and read the liter card.

Can I calculate the weight of water in a pipe?

Yes. The default is 8.34 lb per US gallon (near 60°F planning density). You can enter another density in lb/US gal for a different liquid.

Does this calculator work for PVC and copper pipe?

Yes. Volume depends on the inside diameter, not the brand name. Standard-pipe mode includes PVC Schedule 40/80, copper Type L/M, steel Schedule 40/80, and PEX SDR-9 from published dimensions.

Can this calculator estimate fill time?

Yes, in Advanced. Enter a flow rate in US gpm or L/min. Time = filled volume ÷ flow. That is a volume/time estimate, not a pump curve.

Does this calculator size a pipe?

No. It only reports how much liquid a given bore and length can hold. Use the pipe sizing calculator for diameter from fixture demand.

Do fittings and valves count?

Not in this model. The math is a straight circular cylinder. Elbows, tees, and valves add a little extra volume.

Can I calculate volume from outside diameter and wall thickness?

Yes. OD + wall mode computes ID = OD − 2 × wall, shows that inside diameter, then reports volume from the cylinder formula.

Related Plumbing Calculators

• Pipe Sizing Calculator — Diameter from fixture demand — not how much water the pipe holds.
• PEX Pipe Calculator — How much PEX tubing to buy after you know the run length.
• Drain Slope Calculator — Fall on a drain run. A sloped drain is usually not full of water.
• Water Heater Calculator — Tank or tankless size — separate from the gallons sitting in the pipe.
• Hot Water Flow Calculator — Peak hot-water GPM if you also need a fill-time estimate.