Calculator · Free
Pipe Volume & Fill Calculator
Calculate the water volume, weight and fill time of a pipe run for flushing and testing.
Volume of 150 ft of 3/4" Copper, Type L
3.77 gal0.50 ft³
0.0251 gal per foot at a 0.785 in. bore.
- Gallons per foot2.51 gal per 100 ft
- 0.0251 gal
- Weight of the waterAt 8.34 lb per gallon — hanger and support load
- 31.5 lb
- Fill or drain timeAt 8.0 gpm with no downstream restriction
- 28 sec
- Velocity at that flowInside the usual 8 ft/s working limit
- 5.3 ft/s
Use this figure for chemical dosing, not just curiosity
A 3.77 gallon system volume is what sets your chlorination dose, your glycol charge and the water you have to displace on a pressure test. On a hydronic loop, getting the glycol ratio wrong in either direction either freezes the loop or gels it.
| Nominal | Inside diameter | Gallons per foot | Gallons per 100 ft | Water weight per 100 ft |
|---|---|---|---|---|
| 1/2" | 0.545 in | 0.0121 | 1.21 | 10.1 lb |
| 3/4" — selected | 0.785 in | 0.0251 | 2.51 | 21.0 lb |
| 1" | 1.025 in | 0.0429 | 4.29 | 35.7 lb |
| 1-1/4" | 1.265 in | 0.0653 | 6.53 | 54.5 lb |
| 1-1/2" | 1.505 in | 0.0924 | 9.24 | 77.1 lb |
| 2" | 1.985 in | 0.1608 | 16.08 | 134.1 lb |
| 2-1/2" | 2.465 in | 0.2479 | 24.79 | 206.8 lb |
| 3" | 2.945 in | 0.3539 | 35.39 | 295.1 lb |
| Measure | Basis | Value |
|---|---|---|
| Gallons | π/4 × d² × length ÷ 231 in³ per gal | 3.77 |
| Cubic feet | Gallons ÷ 7.481 | 0.504 |
| Liters | Gallons × 3.785 | 14.3 |
| Water weight | Gallons × 8.34 lb | 31.5 lb |
| Fill or drain time | Gallons ÷ 8.0 gpm | 28 sec |
What this assumes
- Uses nominal pipe inside diameters for common copper, PEX, PVC and steel sizes.
- Water density is taken at 8.34 lb per gallon at room temperature.
- Fill time assumes constant supply flow with no restriction downstream.
Understanding the result
Why volume matters on service work
Chlorination, glycol charging and system flushing all require knowing how much liquid a system holds. Guessing means either wasting chemical or under-treating the system, and on a hydronic loop an incorrect glycol ratio can either freeze or gel.
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