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. | |||
Water Weight Per Inch of Depth
For vertical cylindrical tanks, knowing how much each inch of water depth weighs helps with structural planning and level gauging. The weight per inch increases with tank diameter.
| Tank Diameter | Gallons Per Inch | Pounds Per Inch | Typical Tank Size |
|---|---|---|---|
| 24" diameter | 1.96 gal/inch | 16.4 lbs/inch | ~50 gallon vertical |
| 30" diameter | 3.06 gal/inch | 25.5 lbs/inch | ~100 gallon vertical |
| 36" diameter | 4.41 gal/inch | 36.8 lbs/inch | ~150–200 gallon |
| 48" diameter | 7.84 gal/inch | 65.4 lbs/inch | ~500 gallon vertical |
| 64" diameter | 13.93 gal/inch | 116.2 lbs/inch | ~1,000 gallon vertical |
| 90" diameter | 27.61 gal/inch | 230.4 lbs/inch | ~2,500 gallon vertical |
| 102" diameter | 35.44 gal/inch | 295.7 lbs/inch | ~5,000 gallon vertical |
| Gallons per inch = π × (diameter/2)² ÷ 231. Pounds per inch = gallons per inch × 8.345. | |||
Floor Load & Structural Planning
The weight of a full water tank is concentrated on the tank's base footprint. For structural planning, calculate the load in pounds per square foot (PSF) and compare to the floor or pad's rated capacity.
| Load (PSF) | Total weight (lbs) ÷ Base area (sq ft) |
| Base area (circle) | π × radius² (in feet) |
| Typical residential floor | 40–50 PSF live load capacity |
| Reinforced concrete slab | 150–300+ PSF capacity |
| Tank Size | Full Water Weight | Base Diameter | Base Area | Floor Load (PSF) | Suitable For |
|---|---|---|---|---|---|
| 100 gallons | 835 lbs | 30" | 4.9 sq ft | 170 PSF | Concrete pad; reinforced slab only |
| 250 gallons | 2,086 lbs | 36" | 7.1 sq ft | 294 PSF | Concrete pad required |
| 500 gallons | 4,173 lbs | 48" | 12.6 sq ft | 331 PSF | Concrete pad; never on wood residential floor |
| 1,000 gallons | 8,345 lbs | 64" | 22.3 sq ft | 374 PSF | Engineered concrete pad minimum |
| 2,500 gallons | 20,863 lbs | 90" | 44.2 sq ft | 472 PSF | Heavy-duty concrete pad; consult engineer |
| 5,000 gallons | 41,725 lbs | 102" | 56.7 sq ft | 736 PSF | Engineered foundation required |
| These are water weight only — add tank empty weight (150–800 lbs depending on size). Residential wood frame floors are NOT rated for tanks over 50–100 gallons without structural reinforcement. Always consult a structural engineer for permanent tank installations over 500 gallons. | |||||
Specific Gravity — Other Liquids vs. Water
The calculator above is calibrated for pure water at 8.345 lbs/gallon. Other liquids are heavier or lighter. Use the specific gravity multiplier to adjust:
| Liquid | Specific Gravity | lbs per Gallon | Notes |
|---|---|---|---|
| Fresh water | 1.000 | 8.345 lbs | Standard reference |
| Seawater | 1.025 | 8.554 lbs | Varies with salinity |
| Diesel fuel | 0.850 | 7.09 lbs | Lighter than water |
| Gasoline | 0.720 | 6.01 lbs | Significantly lighter |
| 12.5% sodium hypochlorite (bleach) | 1.168 | 9.75 lbs | Common bulk bleach |
| Liquid fertilizer (UAN 32%) | 1.320 | 11.00 lbs | Significantly heavier than water |
| Milk | 1.030 | 8.60 lbs | Slightly heavier than water |
| To calculate weight of any liquid: gallons × 8.345 × specific gravity = pounds. Always verify specific gravity from the product's safety data sheet (SDS). | |||
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.
300 gallons of water weighs approximately 2,503.5 pounds (1,135.5 kg) — just over 1.25 US tons. A 300-gallon poly tank typically weighs 65–90 lbs empty, bringing total loaded weight to around 2,570–2,595 lbs. This requires a concrete pad or compacted gravel base for permanent installation — a standard residential wood floor is not rated for this load.
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.
5,000 gallons of water weighs approximately 41,725 pounds (18,925 kg) — nearly 21 US tons. A 5,000-gallon poly tank weighs approximately 450–650 lbs empty, bringing total loaded weight to around 42,200–42,400 lbs. An engineered concrete pad is required. A fully loaded 5,000-gallon tank is heavier than most commercial box trucks and requires professional installation planning.
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.
A 275-gallon IBC tote holds 275 × 8.345 = 2,295 lbs of water. The tote itself (HDPE bottle plus galvanized steel cage and pallet) weighs approximately 115–130 lbs empty. Total loaded weight is approximately 2,410–2,425 lbs. Always verify the ground or floor can support this load before filling — an IBC tote on a residential wood deck or unsupported floor can cause structural failure.
Water and wastewater treatment professional with 18+ years of hands-on industry experience. Holds a Grade IV Wastewater Certification and has operated systems ranging from frac tank flow equalization setups to refinery DAF units and metals pretreatment facilities. He founded TankAuthority to bring real operator knowledge to water storage decisions.