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SZ-01Sizing · Plumbing

Pipe volume calculator

Gallons and liters in a run of copper, PEX, PVC, CPVC or steel pipe, from each size’s published inside diameter — not its nominal size. Add runs, time the hot-water wait, print the table.

Gallons in the run

Example: 35 ft of 3/4" and 15 ft of 1/2" Type L copper to a bathroom faucet. Change any number.

Water in the pipe Example

1.06 gallons (4.02 liters) in 2 runs, 50 ft. First hot water no sooner than 29 seconds at 2.2 gpm.

4.02 liters in 2 runs, 50 ft

Change the pipe
Inside diameters, to scale3/4" Copper Type L (run 1) beside the next sizes
Pipe volume drawing for the example: sections to scale and the run drawn to lengthCopper Type L sections at one scale: 5/8 inch 0.666 inch inside diameter, 1.81 gallons per 100 feet; 3/4 inch 0.785 inch inside diameter, 2.51 gallons per 100 feet; 1 inch 1.025 inch inside diameter, 4.29 gallons per 100 feet. run 1: 3/4 inch Copper Type L, 35 ft, 0.880 gal; run 2: 1/2 inch Copper Type L, 15 ft, 0.182 gal. Total 50 ft, 1.06 gal. At 2.2 gpm the first hot water can arrive after 29 seconds at the earliest.0.6665/8"1.81gal / 100 ft0.7853/4"2.51gal / 100 ft1.0251"4.29gal / 100 ftRuns, drawn to length0.880 gal0.182 gal35 ft15 ft50 ft =1.06 galFirst hot water, at 2.2 gpm0 s10 s20 s29 s0.5 gal · WaterSense targetreached at 19.9 ft · a design target, not code
  1. 3/4" Copper Type L35 ft · ID 0.785 in · 0.0251 gal/ft0.880 gal
  2. 1/2" Copper Type L15 ft · ID 0.545 in · 0.0121 gal/ft0.182 gal
  3. Total 50 ft1.06 gal

Inside diameter: CDA Copper Tube Handbook Table 14.2b. Volume is computed from the inside diameter, never the nominal size: gallons per foot = π/4 × ID² × 12 ÷ 231.

Water weight
8.9 lb4.0 kg · water at 60 °F
Per 100 ft
2.12 galaverage of the runs
Minimum wait
29 sat 2.2 gpm

0.0408 × 0.785² × 35 ft + 0.0408 × 0.545² × 15 ft = 1.06 gal

Minimum wait: it assumes the cold water leaves as a slug and the first hot water arrives hot. Pipe walls and fittings absorb heat, so the real wait is longer.

Already showing the example.

What changes the gallons

  • The run holds 2.1× WaterSense’s design target of 0.5 gal between the heater and a fixture (a target, not a code requirement); the first 0.5 gal is used up 19.9 ft in.
  • The same runs in PEX (CTS, SDR 9) would hold 0.781 gal (−26%), a minimum wait of 21 s.
  • Run 1 one size up (1") would add 0.620 gal and 17 s to the wait.

Change the numbers

Units: feet and gpm, or meters and L/min
Pipe runs
  1. Run 1

    ID 0.785 in

    Developed length, feet

  2. Run 2

    ID 0.545 in

    Developed length, feet

Hot water wait

Stated maximums, not measured flows; real flows are often lower.

Bathroom faucet, federal maximum: 10 CFR 430.32(o), 2.2 gpm at 60 psi.

Chlorine fill

In the pipe: 1.06 gal in 50 ft · minimum wait 29 s. Back to the result

Gallons per foot: Copper Type L

Every size, computed from the inside diameters in CDA Copper Tube Handbook Table 14.2b. Gallons per foot = 0.0408 × ID². Follows the material of the run you’re editing.

Copper Type L: inside diameter and water volume per length for each nominal size, computed from CDA Copper Tube Handbook Table 14.2b.
NominalID, inGal/ftGal/100 ftL/mFt per 0.5 gal
1/4"0.3150.004050.4050.0503123.5
3/8"0.4300.007540.7540.093766.3
1/2"0.5450.01211.210.15141.3
5/8"0.6660.01811.810.22527.6
3/4"in your run0.7850.02512.510.31219.9
1"1.0250.04294.290.53211.7
1-1/4"1.2650.06536.530.8117.7
1-1/2"1.5050.09249.241.155.4
2"1.9850.16116.082.003.1
2-1/2"2.4650.24824.793.082
3"2.9450.35435.394.391.4
3-1/2"3.4250.47947.865.941
4"3.9050.62262.227.730.8
5"4.8750.97096.9612.040.5
6"5.8451.39139.417.310.4
8"7.7252.43243.530.240.2
10"9.6253.78378.046.940.1
12"11.5655.46545.767.770.1

“Ft per 0.5 gal” is the length that holds WaterSense’s 0.5-gallon hot water delivery target (a design target, not a code limit). Pipe only: fittings, valves, fixtures and the water heater are not included.

How the math works

Volume depends on the inside diameter, and a “3/4-inch” pipe has an inside diameter anywhere from 0.671 in (PEX) to 0.824 in (steel Schedule 40). So the calculator looks up the published inside diameter for the exact material and size, and never multiplies by the nominal size.

  1. Inside diameterID = the published inside diameter, inShown next to every result with the document it came from. Plastic pipe IDs are the published averages.
  2. Gallons per footπ ÷ 4 × ID² × 12 ÷ 231 = 0.0408 × ID²231 cubic inches make one U.S. gallon, exactly (NIST Handbook 44).
  3. Gallons in the pipegal/ft × length, added up over every runMetric lengths are converted to feet first (1 ft = 0.3048 m); nothing is rounded until it is shown.
  4. Litersgallons × 3.785411784
  5. Weight of the watergallons × 8.34 lb; × 0.45359237 for kgWater only, at about 60 °F; hot water weighs about 1.6% less at 140 °F (USGS).
  6. Minimum hot water waitgallons ÷ gpm × 60 = secondsMinimum wait: it assumes the cold water leaves as a slug and the first hot water arrives hot. Pipe walls and fittings absorb heat, so the real wait is longer.
  7. Bleach, approximatepipe gallons × ppm ÷ (label % × 10,000)Approximate — confirm with a test kit. Unconfirmed: Treats the label % (sodium hypochlorite) as grams of available chlorine per 100 mL and ignores bleach density and the hypochlorite-to-chlorine conversion; no source read states either factor.
Where every number comes from 22 values, each with its source
ID, Copper Type K
1/4" to 12"CDA Copper Tube Handbook Table 14.2a
ID, Copper Type L
1/4" to 12"CDA Copper Tube Handbook Table 14.2b
ID, Copper Type M
3/8" to 12"CDA Copper Tube Handbook Table 14.2c
ID, PEX (CTS, SDR 9)
3/8" to 2"PPI PEX Design Guide Table 7.11; Uponor submittal (1/2"–2")
ID, PVC Schedule 40
1/4" to 12"Spears Dimensions & Pressure Ratings (avg I.D.); GF Harvel Clear PVC
ID, PVC Schedule 80
1/4" to 12"Spears (avg I.D.); GF Harvel PVC 80 specification
ID, CPVC Schedule 40
1/4" to 12"Spears CPVC Sch 40 (avg I.D., same as PVC Sch 40)
ID, CPVC Schedule 80
1/4" to 12"Spears CPVC Sch 80 (avg I.D., same as PVC Sch 80)
ID, CPVC CTS (SDR 11)
1/2" to 2"Spears SDR 11 CTS (avg I.D.); Charlotte FlowGuard Gold walls
ID, Steel Schedule 40
1/2" to 10"Wheatland Tube Standard Pipe (ASTM A53 / ASME B36.10M). Unconfirmed: Galvanized pipe: no source read says whether the zinc coating changes the inside diameter; the same IDs are used for black and galvanized Schedule 40.
Cubic inches per gallon
231 (exact)NIST Handbook 44 (2026), Appendix C: "231 cubic inches (exactly)"
Liters per gallon
3.785411784NIST Handbook 44 (2026), Appendix C
Meters per foot
0.3048NIST SP 811 (Guide to the SI), Appendix B.8
Water weight
8.34 lb per gallonSite arithmetic: USGS Water Density, 62.366 lb/ft³ at 60 °F ÷ 7.480519 gal/ft³ (NIST) = 8.337, rounded. Water only, at about 60 °F; hot water weighs about 1.6% less at 140 °F (USGS).
Kilograms per pound
0.45359237NIST SP 811 (Guide to the SI), Appendix B.8 (prints 0.4535924)
Showerhead, federal maximum
2.5 gpm10 CFR 430.32 (eCFR, version 2026-10-01)(p): 2.5 gpm at 80 psi
Showerhead, WaterSense maximum
2 gpmU.S. EPA WaterSense, Showerheads
Bathroom faucet, federal maximum
2.2 gpm10 CFR 430.32 (eCFR, version 2026-10-01)(o): 2.2 gpm at 60 psi
Bathroom faucet, WaterSense maximum
1.5 gpmU.S. EPA WaterSense, Bathroom Faucets
Kitchen faucet, federal maximum
2.2 gpm10 CFR 430.32 (eCFR, version 2026-10-01)(o): 2.2 gpm at 60 psi
Hot water delivery target
0.5 gal or lessU.S. EPA WaterSense, Hot Water Delivery tech sheet EPA-832-F-23-016 (July 2023). A design target, not a code requirement
Bleach strengths
6% or 8.25% on the labelU.S. EPA, Emergency Disinfection of Drinking Water (label strengths 6% or 8.25%)

Before you use the number

  • Pipe only. Fittings, valves, fixtures and the water heater are not counted; a tank heater holds far more than the piping to it.
  • The wait is a floor, not a forecast. The pipe walls and fittings soak up heat, so the real wait is longer. WaterSense’s field check: at the farthest fixture, run hot water into a bucket until the temperature rises 10 °F, then measure the water collected.
  • Codes limit length, not volume. The model 2024 International Plumbing Code (§607.2) limits the developed length of hot or tempered water piping from the source to a fixture to 50 ft, counting recirculating and heat-traced piping as sources. States adopt different editions and amendments, and some build on the Uniform Plumbing Code instead; check the code your jurisdiction enforces.
  • Disinfection is set by the authority having jurisdiction. The health authority, the water purveyor or the building department decides how a system is flushed and disinfected. The bleach figure is approximate: confirm the concentration with a chlorine test kit.
  • Weight is water only, at about 60 °F. Hot water weighs a little less (about 1.6% less at 140 °F, USGS); the pipe’s own weight is not included.
  • Two CDA volume cells will not match. The Copper Tube Handbook prints 0.571 gal/ft for 4″ Type L, but its own 3.905 in ID gives 0.622; its 5/8″ Type L row repeats Type K. Every volume here is computed from the ID.

Sources

  1. Copper Tube Handbook (A4015-26/24), Tables 14.2a–cCopper Development Association
  2. Design Guide: Residential PEX Water Supply Plumbing Systems, 2nd ed., Chapter 7 (Table 7.11)Plastics Pipe Institute
  3. Uponor AquaPEX submittal sheet (inner and outer diameters, 1/2"–2")Uponor North America (hosted by SupplyHouse)
  4. Dimensions & Pressure Ratings (average I.D. for PVC, CPVC and CPVC CTS)Spears Manufacturing
  5. PVC Schedule 80 Pipe Product SpecificationsGF Piping Systems (Harvel)
  6. Pressure Pipe and Fittings Dimensional Catalog DC-PRCharlotte Pipe and Foundry
  7. Standard Pipe brochure (Schedule 40, ASTM A53)Wheatland Tube
  8. Handbook 44 (2026), Appendix C: General Tables of Units of MeasurementNational Institute of Standards and Technology
  9. NIST Guide to the SI, Appendix B.8: Factors for units listed alphabeticallyNational Institute of Standards and Technology
  10. Water DensityU.S. Geological Survey
  11. Hot Water Delivery (WaterSense Labeled Homes tech sheet EPA-832-F-23-016)U.S. EPA WaterSense
  12. 10 CFR 430.32: Energy and water conservation standards (showerheads, faucets)eCFR (Office of the Federal Register)
  13. ShowerheadsU.S. EPA WaterSense
  14. Bathroom FaucetsU.S. EPA WaterSense
  15. 2024 International Plumbing Code, Chapter 6: Water Supply and Distribution (§§607.2, 610.1)International Code Council, Digital Codes (free to read)
  16. Read IAPMO Codes Online (Uniform Plumbing Code)IAPMO
  17. Emergency Disinfection of Drinking Water (bleach label strengths)U.S. EPA

  • 3.01Guide

    Gallons in a Pipe by Size: Copper, PEX, PVC and CPVC

    Gallons per 100 feet for copper K, L and M, PEX, PVC Schedule 40 and CPVC, computed from published inside diameters, with wait-time and flushing math.

    π ÷ 4 × ID² × 12 ÷ 231 = 0.0408 × ID²

    Length
    7 min
    Updated

  • 3.02Guide

    How to Price a Water Heater Replacement From Your Numbers

    A contractor-side worked example: heater, parts, permit, haul-away and labor at your shop rate, a margin check, and why average cost pages miss your job.

    $1,437.50 ÷ $1,085 − 1 = 32.49%

    Length
    7 min
    Updated

Tools for the job

Tool listPlumbing4 itemsSpecs read

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  1. Press and expansion toolsMilwaukee 2922-22

    M18 FORCE LOGIC Press Tool w/ ONE-KEY w/ 1/2"-2" CTS Jaws

    • Milwaukee lists 1/2 in. to 4 in. press capacity and compatibility with more than 20 fitting systems.

    Specs: Milwaukee product page, read

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  2. Press and expansion toolsMilwaukee 2473-22

    M12 FORCE LOGIC Press Tool Kit with Jaws

    • Weighs 3.8 lb and delivers up to 5,400 lb of force in an in-line, one-handed design.

    Specs: Milwaukee product page, read

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  3. Threading and cuttingMilwaukee 2870-22

    M18 FUEL Compact Pipe Threader w/ ONE-KEY w/ 1/2"-1-1/4" Compact NPT Forged Aluminum Die Heads

    • Threads up to 1-1/4 in. black iron, stainless steel and rigid metal conduit.

    Specs: Milwaukee product page, read

    View on Amazon for Milwaukee 2870-22(paid link)

  4. Testing and water heater serviceRIDGID 1450

    1450 Pressure Test Pump (Catalog No. 50557)

    • Hydrostatic test pump for systems up to 725 PSI: heating, sprinkler, compressed air, refrigeration and other small-bore piping.

    Specs: RIDGID product page, read

    View on Amazon for RIDGID 1450(paid link)

How tools are chosen for gear listsAll 16 plumbing tools