Pipe Volume Calculator
Calculate how much water any pipe holds. Enter inner diameter and length for gallons, liters, cubic feet, and system totals.
Pipe volume is the amount of fluid a pipe can hold, found by treating the bore as a cylinder: inner diameter and length go into V = π × (d ÷ 2)² × L. This free pipe capacity calculator returns gallons, liters, cubic feet, water weight, fill time, and antifreeze doses, with multi-segment mode to total your whole plumbing system.
Pipe volume is the amount of water or fluid inside a pipe, calculated from its inner diameter and length using the cylinder formula. Enter ID and length to get volume in gallons, liters, or cubic feet, the same math plumbers, HVAC techs, and irrigation contractors use for winterizing, hydronic fills, and pressure tests.
Whether you are dosing glycol in a boiler loop or sizing a pump for an irrigation main, you need the volume of water in a pipe, not a guess from nominal size on the label. Once you have your numbers, Invoice Mama makes it easy to build a professional plumbing estimate and send it straight to your client.
How to Calculate Pipe Volume
Three steps from nominal size on the truck to gallons in the line, same workflow as the HowTo schema on this page.
- 1
Find inner diameter (ID)
Use the preset dropdown for Schedule 40, Schedule 80, PEX, or Type K copper, or look up ID in a pipe dimensions chart. Measure the bore if the material is unknown.
- 2
Measure pipe length
Measure the full run in feet or meters. For whole-building totals, add each branch as its own segment in multi-segment mode.
- 3
Apply the formula
V = π × (d ÷ 2)² × L. The calculator outputs gallons, liters, cubic feet, cubic inches, cubic meters, and water weight in real time.
Pipe Volume Formula
Cylinder math: the pipe volume formula every trade school teaches on day one.
d is inner diameter, L is length. Keep units consistent: inches with feet (convert feet to inches by × 12), or millimeters with meters. The pipe fill volume grows with the square of diameter, a small ID error at 4-inch mains becomes a big gallon miss on long runs.
Example: 2-inch Schedule 40 (ID 2.067 in) × 50 ft run. Length in inches = 600. Volume = 3.14159 × (1.0335)² × 600 ≈ 2,010 in³ ≈ 8.7 gallons.
Pipe Volume Per Foot - Reference Chart
Schedule 40 inner diameter: gallons, liters, and water weight per linear foot.
Quick lookup for water volume in pipe per foot of length. Values use Schedule 40 ID, the most common spec on residential and light commercial jobs. For schedule 40 pipe volume on long mains, multiply gallons per foot by your measured length.
Nominal size | Gallons/ft | Liters/ft | Water weight (lb/ft) |
|---|---|---|---|
| 1/2″ | 0.0158 | 0.060 | 0.132 |
| 3/4″ | 0.0277 | 0.105 | 0.231 |
| 1″ | 0.0449 | 0.170 | 0.374 |
| 1-1/4″ | 0.0777 | 0.294 | 0.648 |
| 1-1/2″ | 0.1058 | 0.400 | 0.882 |
| 2″ | 0.1743 | 0.660 | 1.454 |
| 2-1/2″ | 0.2487 | 0.941 | 2.074 |
| 3″ | 0.3840 | 1.454 | 3.203 |
| 4″ | 0.6613 | 2.503 | 5.515 |
| 6″ | 1.5008 | 5.681 | 12.517 |
Schedule 40 vs Schedule 80 Inner Diameter
Nominal pipe size inner diameter comparison, PEX and Type K copper included.
Nominal | Sch 40 ID (in) | Sch 80 ID (in) | PEX ID (in) | Type K Cu ID (in) |
|---|---|---|---|---|
| 1/2″ | 0.622 | 0.546 | 0.475 | 0.527 |
| 3/4″ | 0.824 | 0.742 | 0.671 | 0.745 |
| 1″ | 1.049 | 0.957 | 0.860 | 0.995 |
| 1-1/4″ | 1.380 | 1.278 | 1.077 | 1.245 |
| 1-1/2″ | 1.610 | 1.500 | 1.265 | 1.481 |
| 2″ | 2.067 | 1.939 | 1.632 | 1.959 |
| 2-1/2″ | 2.469 | 2.323 | - | 2.435 |
| 3″ | 3.068 | 2.900 | - | 2.907 |
| 4″ | 4.026 | 3.826 | - | 3.857 |
| 6″ | 6.065 | 5.761 | - | 5.741 |
Thicker Schedule 80 walls steal bore volume at every size. On a 6-inch main, Sch 40 ID is 6.065 in versus 5.761 in for Sch 80, that is real money in glycol and fill water on a commercial hydronic loop.
Inner Diameter vs Outer Diameter
Why ID is non-negotiable for pipe capacity calculator results.
Nominal pipe size (NPS) labels the outside of the pipe: 2-inch copper is not 2 inches on the inside. Wall thickness varies by schedule and material, so two "2-inch" pipes can hold noticeably different gallons per foot. A pipe capacity calculator only works when you feed it inner diameter.
- Use inner diameterWater touches the bore, not the outside of the fitting.
- Match material scheduleSch 40, Sch 80, PEX, and copper all have different IDs at the same nominal size.
- Verify in the fieldOlder scale or unknown material? Measure ID with calipers on a clean cut.
- Do not trust OD labelsOuter diameter will overstate cubic feet of water in pipe every single time.
Unit Conversion Quick Reference
Cubic inches to gallons, liters, cubic feet, and cubic meters.
From | To | Multiply by |
|---|---|---|
| Cubic inches | US gallons | ÷ 231 |
| US gallons | Liters | × 3.78541 |
| Cubic inches | Cubic feet | ÷ 1,728 |
| Cubic feet | Cubic meters | × 0.0283168 |
| Cubic meters | Liters | × 1,000 |
| US gallons (water) | Pounds | × 8.34 |
| Liters (water) | Kilograms | × 1 |
Winterizing a Plumbing System - Antifreeze Calculation
Worked example: seasonal cottage with multiple pipe sizes.
A lake cottage has 120 ft of 3/4-inch PEX supply (ID 0.671 in) plus 40 ft of 1/2-inch branch (ID 0.475 in). Segment one: ~1.53 gal. Segment two: ~0.41 gal. System total ≈ 1.94 gallons. For a 50% propylene glycol mix, you need about 0.97 gallons of concentrate, plus whatever is in the water heater and traps. Multi-segment mode catches both runs; thats easier than doing two calculator passes on site.
HVAC Hydronic Systems - Glycol Dosing & Expansion Tank Sizing
Worked example: light commercial boiler loop.
A small office boiler loop: 200 ft of 2-inch Schedule 40 supply and return combined (400 ft total at ID 2.067 in) holds about 65 gallons. Add 15 gallons for the boiler and coils → 80 gallons system volume. At 30% glycol for freeze protection to -10°F, you need 24 gallons of antifreeze concentrate on a drained fill. Expansion tank sizing uses this same total. Consult manufacturer charts for acceptance volume. For airflow on the same job, see our HVAC CFM calculator for ventilation loads on mixed mechanical bids.
Irrigation System Design - Fill Time & Pump Sizing
Worked example: main line fill after winter drain.
An irrigation main: 800 ft of 4-inch PVC Schedule 40 (ID 4.026 in) holds about 522 gallons. A fill pump at 25 GPM needs roughly 21 minutes to charge the main, not counting air purge time at risers. Knowing gallons in a pipe upfront keeps you from undersizing the pump or quoting a one-hour fill when the client watches the clock.
Pressure Testing - Water Volume in the Line
Worked example: commercial domestic water pressure test.
Before a hydrostatic test on 600 ft of 6-inch Schedule 40 (ID 6.065 in), calculate fill volume: about 88 gallons in the pipe alone. Test procedures often require holding pressure for 2 hours, so you need enough make-up water on standby and a sense of how much volume you are pressurizing. Pair volume math with your labor cost calculator when quoting test-and-inspect labor on the same ticket.
Multi-Segment System Volume - Whole-Building Totals
The feature other pipe volume calculators skip.
Real jobs are never one straight stick of pipe. Toggle multi-segment mode, add each run with its own diameter and length, and read a running system total in gallons and liters. It is the fastest way to answer "how much water is in my whole plumbing system" from your phone in a crawlspace, then turn that number into line items with our free invoice generator when the job is done.
Frequently Asked Questions
Pipe volume formula, gallons per foot, ID vs OD, and system totals
How do you calculate the volume of a pipe?
Pipe volume uses the cylinder formula: V = π × (d ÷ 2)² × L, where d is inner diameter and L is length in matching units. Convert inches and feet for imperial, or millimeters and meters for metric. Divide cubic inches by 231 for US gallons, or read liters from cubic meters × 1,000. Always use inner diameter, not outer.
What is the pipe volume formula?
The standard pipe volume formula is V = π × r² × h, equivalent to V = π × (d ÷ 2)² × L. Here r is inner radius, h is pipe length, and d is inner diameter. It assumes a straight circular bore filled with fluid. For multiple runs, calculate each segment and add the volumes for a system total.
How do you calculate pipe diameter from a known volume?
Rearrange the cylinder formula: d = 2 × √(V ÷ (π × L)). Convert volume and length to the same unit family first, for example, cubic inches and inches, or gallons and feet via 231 in³ per gallon. Our reverse calculator below the main tool solves for inner diameter in inches and millimeters when you enter volume and length.
How many gallons are in a 2-inch pipe per 100 feet?
A 2-inch Schedule 40 pipe (2.067-inch inner diameter) holds about 17.4 US gallons per 100 feet of length. That is roughly 0.163 gallons per foot. Heavier Schedule 80 walls reduce ID to 1.939 inches, dropping capacity to about 14.3 gallons per 100 feet. PEX and copper IDs differ slightly.
How many gallons are in a 4-inch pipe per 100 feet?
A 4-inch Schedule 40 pipe (4.026-inch ID) holds about 66.1 US gallons per 100 feet, near 0.653 gallons per foot. Schedule 80 at 3.826-inch ID holds roughly 58.9 gallons per 100 feet. Capacity scales with the square of diameter, so doubling pipe size quadruples volume per foot.
Should I use inner diameter or outer diameter for pipe volume?
Always use inner diameter (ID) for pipe volume and water capacity calculations. Outer diameter includes pipe wall thickness and describes physical size, not the space water occupies. Using OD is the number-one mistake on job sites and will overstate gallons, antifreeze doses, and hydronic fill volumes every time.
Who uses a pipe volume calculator?
Plumbers, HVAC technicians, irrigation contractors, pool service techs, fire sprinkler fitters, and mechanical engineers use pipe volume calculators daily. They size glycol doses, estimate fill times, plan pump capacity, and total water in long mains. Construction estimators pair volume math with material takeoffs when quoting repipes, boiler loops, and seasonal winterizing work.
What is the difference between Schedule 40 and Schedule 80 pipe volume?
Schedule 80 has thicker walls than Schedule 40, so the inner diameter is smaller at the same nominal size. A 2-inch Sch 40 ID is 2.067 inches versus 1.939 inches for Sch 80, about 13% less water per foot. For winterizing or glycol dosing, using Sch 40 tables on Sch 80 pipe leaves you short.
How do I calculate how much antifreeze I need for my pipes?
First calculate total pipe water volume in gallons or liters. Multiply by your target antifreeze concentration as a decimal: 50% solution needs concentrate equal to half the system volume if starting from water. Add branch lines and equipment volumes. Our calculator shows antifreeze quantity when you enter a concentration percentage.
How does pipe volume relate to water pressure?
Pipe volume and water pressure are related but not the same calculation. Volume is how much fluid the bore holds; pressure depends on pump head, elevation, flow rate, and friction loss along the run. Wider pipes carry more volume and usually lower resistance, while long narrow runs lose pressure to friction. Size both capacity and diameter for the job.
How do I calculate the volume of water in my entire plumbing system?
List every pipe run with its inner diameter and length, including mains, branches, risers, and dead legs. Calculate each segment with the cylinder formula and sum the totals. Multi-segment mode on this calculator builds that bill of materials on your phone and shows a running system total no single-run tool offers.
How do I calculate pipe volume for an HVAC hydronic system?
Measure supply and return piping, boiler loops, and terminal unit connections using each pipe size inner diameter. Sum segment volumes for total system water content. That total drives glycol concentration, expansion tank sizing, and fill time. Pair this with our HVAC CFM calculator when duct and hydronic work overlap on the same bid.
Can I calculate pipe volume in liters instead of gallons?
Yes. Switch to metric mode and enter inner diameter in millimeters and length in meters. Results show liters prominently alongside US gallons, cubic meters, and cubic feet. One liter of water weighs about one kilogram, which simplifies hydronic and irrigation math outside the United States.
Explore More Free Calculators
Professional tools for contractors and tradespeople
Once you know gallons in the line, Invoice Mama helps you build a professional plumbing or HVAC estimate and send it to your client in seconds.