Based on 8.345 lbs per US gallon at 68°F (20°C room temperature)
How Much Does Water Weigh?
Water weighs 8.345 pounds per US gallon at standard room temperature (68°F / 20°C). This is the number used in tank engineering, plumbing, and water system design.
Water weight varies slightly with temperature — at 32°F (freezing), a gallon of water weighs 8.345 lbs. At 212°F (boiling), it drops to approximately 7.996 lbs per gallon. For practical purposes in tank sizing, 8.345 lbs/gal is the accepted standard.
Common Tank Water Weight Reference
Use this table as a quick reference for the most common water storage tank sizes. For tanks not listed, use the calculator above.
| Tank Size | Water Weight (lbs) | Water Weight (kg) | US Tons | Guide |
|---|---|---|---|---|
| 50 gallons | 417 lbs | 189 kg | 0.21 tons | 50 Gal Guide |
| 100 gallons | 835 lbs | 379 kg | 0.42 tons | 100 Gal Guide |
| 150 gallons | 1,252 lbs | 568 kg | 0.63 tons | 150 Gal Guide |
| 200 gallons | 1,669 lbs | 757 kg | 0.83 tons | 200 Gal Guide |
| 250 gallons | 2,086 lbs | 946 kg | 1.04 tons | 250 Gal Guide |
| 500 gallons | 4,173 lbs | 1,893 kg | 2.09 tons | 500 Gal Guide |
| 750 gallons | 6,259 lbs | 2,839 kg | 3.13 tons | 750 Gal Guide |
| 1,000 gallons | 8,345 lbs | 3,785 kg | 4.17 tons | 1,000 Gal Guide |
| 1,500 gallons | 12,518 lbs | 5,678 kg | 6.26 tons | 1,500 Gal Guide |
| 2,000 gallons | 16,690 lbs | 7,570 kg | 8.35 tons | 2,000 Gal Guide |
| 2,500 gallons | 20,863 lbs | 9,463 kg | 10.43 tons | 2,500 Gal Guide |
| 5,000 gallons | 41,725 lbs | 18,925 kg | 20.86 tons | 5,000 Gal Guide |
| 10,000 gallons | 83,450 lbs | 37,850 kg | 41.73 tons | 10,000 Gal Guide |
| Calculated at 8.345 lbs/gallon. Weights are for water only — add tank empty weight for total loaded weight. | ||||
The Formula
The formula is straightforward:
| Weight in lbs | Gallons × 8.345 |
| Weight in kg | Gallons × 3.785 |
| Weight in US tons | Gallons × 0.004172 |
Example: A 500-gallon water tank holds 500 × 8.345 = 4,172.5 pounds of water. A standard poly tank at that size weighs approximately 110–160 lbs empty, so total loaded weight is roughly 4,290–4,330 lbs.
Why Water Weight Matters
Knowing the weight of a full water tank matters for several practical reasons:
- Structural load: Floors, concrete pads, and trailer beds must be rated for the total loaded weight. A 1,000-gallon tank on a residential floor can cause structural damage if the subfloor isn't reinforced.
- Trailer capacity: When mounting a tank on a trailer, the GVWR must exceed the total loaded weight. A 500-gallon tank trailer needs to handle 4,173 lbs of water plus the trailer and tank weight.
- Pump selection: Submersible and transfer pumps are rated for head pressure, which depends on the height of the water column. Taller tanks create more head pressure.
- Shipping & delivery: Large tanks (2,500+ gallons) often ship empty. Know what a full tank weighs before requesting freight delivery or setting up on a permanent pad.
Water Weight by Temperature
Water density changes with temperature. For most tank applications this difference is negligible, but for precision calculations:
| Temperature | lbs per Gallon | kg per Liter | Notes |
|---|---|---|---|
| 32°F (0°C) | 8.345 lbs | 0.9998 kg/L | Near freezing |
| 39°F (4°C) | 8.345 lbs | 1.0000 kg/L | Maximum density |
| 68°F (20°C) | 8.330 lbs | 0.9982 kg/L | Standard (this calculator) |
| 104°F (40°C) | 8.278 lbs | 0.9922 kg/L | Hot water tank temp |
| 212°F (100°C) | 7.996 lbs | 0.9584 kg/L | Boiling point |
| The 8.345 lbs/gallon standard is used for tank engineering and design at room temperature. | |||
Frequently Asked Questions
One US gallon of water weighs 8.345 pounds (3.785 kg) at room temperature (68°F / 20°C). This is the standard weight used in engineering calculations for water systems, tank sizing, and plumbing design.
150 gallons of water weighs approximately 1,251.75 pounds (567.75 kg). At this weight, a proper concrete pad or reinforced base is recommended for long-term storage.
500 gallons of water weighs approximately 4,172.5 pounds (1,892.5 kg) — just over 2 US tons. For reference, a standard pickup truck (F-150) has a maximum payload of around 1,700–2,000 lbs, so a 500-gallon full tank cannot be safely transported in a standard pickup bed.
1,000 gallons of water weighs approximately 8,345 pounds (3,785 kg), or about 4.17 US tons. A 1,000-gallon poly tank typically weighs 150–250 lbs empty, so total loaded weight is around 8,500–8,600 lbs. This requires a commercial-grade concrete pad or reinforced ground for permanent installation.
Yes, but only slightly. Water is densest at 39°F (4°C) at 8.345 lbs/gallon, and becomes less dense as it warms. At 212°F (boiling), it drops to approximately 7.996 lbs/gallon — a difference of less than 4%. For standard tank calculations, 8.345 lbs/gallon is used for all temperatures.