Pipe Volume Calculator
Water in the bore — gallons, per-foot, weight, and how long the run takes to fill and to flush, by the true inside diameter.
Pipe Volume Calculator
Results recalculate instantly on every keystroke. Nothing you type is transmitted.
What this result does not account for
- Sch 40 IDs charted — other schedules need their own bore.
- Full-bore volume only; no partial-flow hydraulics.
- No friction, velocity or pressure-drop modeling.
In short: 100 ft of 2-inch Schedule 40 (ID 2.067 in): 4,026.73 in³ = 17.43 gallons, 0.1743 gal per foot, 145.4 lb of water, 3.49 minutes to fill at 5 GPM, 34.9-52.3 gallons to flush. Volume squares with the bore — 1-inch pipe holds just 4.49 gallons per hundred feet.
Formula
V = π × (ID ÷ 2)² × L(in)
gallons = in³ ÷ 231
gal/ft = ID² × 0.0408
fill = gallons ÷ GPM; flush = 2-3 volumes
[('231', 'cubic inches per US gallon, exact'), ('0.0408', 'π×12÷(4×231) — the gal/ft shortcut'), ('2.067', 'the real bore behind the “2-inch” label'), ('8.34', 'pounds per gallon of water')]
Worked Example
- Find the true inside diameter — the chart or the calipers, never the label.
- Multiply length by 12; apply πr²L.
- Divide by 231 for gallons.
- Weigh it at 8.34 lb per gallon.
- Time the fill at your GPM; flush 2-3 volumes.
2-in Sch 40, 100 ft: π × 1.0335² × 1,200 = 4,026.73 in³ → 17.43 gal → 145.4 lb → 3.49 min at 5 GPM; flush 34.9-52.3 gal. The shortcut agrees: 2.067² × 0.0408 = 0.1743 gal/ft.
Strengths & Limits Of This Model
Where this engine is strong
- Sch 40 bore chart as chips — the label trap closed
- Shortcut shown AS the exact law, not instead of it
- Fill, flush and hanger weight from one bore
Where it stops
- No Sch 80 / CID chart rows
- No flow dynamics
Practical Use Cases
Hydronic systems
System volume for expansion tanks.
Winterizing
Gallons that must drain down.
Chemical dosing
Pipe volume in the dose math.
Pressure testing
Fill volume and hold time.
Priming
Gallons before the heads run wet.
Methodology & Editorial Standards
One cylinder law on the TRUE bore: V = π(ID/2)²L in cubic inches, ÷ 231 to US gallons, with the Sch 40 ID chart as free-entry chips (0.622 → 6.065). The gal/ft shortcut (ID² × 0.0408) is shown as the same π-law to six decimals. Weight at 8.34 lb/gal; fill time at the entered GPM; flush printed as the industry’s 2-3 volumes. Nonpositive bores, lengths or flows refused; bores past 48 in refused as tunnels.
Computation runs in IEEE-754 double precision at full internal precision; rounding to two decimal places occurs strictly at the display layer, so no cumulative drift enters the result. All monetary outputs use accounting presentation — grouped thousands, two decimals, negatives in parentheses — so figures can be transcribed directly into a model or working paper. Division-by-zero and out-of-domain inputs return an em-dash rather than a misleading number.
This engine was reconciled against an independent reference implementation and hand-verified for the worked example above before release. Our full five-stage review process is published on the About Us page.
Disclaimer. This calculator is provided for informational and modelling purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Verify all figures with a qualified professional before acting on them.
Pipe Volume Calculator — 8 Expert FAQs
8 analyst-written answers to the questions practitioners actually ask — optimised for voice and answer-engine retrieval.
How do I calculate the volume of a pipe?
Treat it as a cylinder of the INSIDE diameter: π × (ID ÷ 2)² × length, in inches, then divide by 231 for US gallons. 100 ft of 2-in Sch 40 is 17.43 gallons.
How many gallons per foot does a pipe hold?
ID in inches squared × 0.0408 — that shortcut is π×12÷(4×231) exactly. A 2.067 bore carries 0.1743 gal/ft; a 1.049 bore, 0.045.
Why not use the nominal size?
Nominal is a label, not a measurement: 2-inch Sch 40 bores 2.067 in, 1-inch bores 1.049, 6-inch bores 6.065. Volume squares the diameter, so label-thinking compounds — measure the bore or use the Sch 40 chart.
How much less does Schedule 80 carry?
Thicker wall, smaller bore: 2-in Sch 80 ID is 1.939 in against Sch 40’s 2.067 — 15.3 vs 17.4 gallons per 100 ft, about 17% less water.
How long does it take to fill a pipe run?
Gallons ÷ GPM. 17.43 gallons at a 5-GPM tap is 3.49 minutes — the same arithmetic behind flushing 2-3 volumes before a water sample.
What does the water in a pipe weigh?
8.34 lb per gallon: those 17.43 gallons hang 145.4 lb on the hangers — real load on long spans and support spacing.
Does doubling the diameter double the water?
Nearly quadruples it — area squares the radius. 1-in pipe holds 4.49 gal per 100 ft; 2-in holds 17.4; 4-in holds 66.
Why does chemical dosing need pipe volume?
A dose concentrates in the WATER, and the pipe is part of the system — treatment math wants total system volume, which is why winterizing, pressure testing and dosing all start with this same bore.