Water Weight Calculator
Accurately calculate the weight of 87 gallons of water (and other volumes)
Water Weight Estimator
Enter the number of US liquid gallons. Default is 87 gallons.
Please enter a valid positive number.
Fresh Water (62°F / 17°C) – Standard
Fresh Water (70°F / 21°C) – Room Temp
Fresh Water (212°F / 100°C) – Boiling
Seawater (Avg. Salinity)
Distilled Water
Ice (Solid)
Density varies by temperature and salinity.
Total Weight (lbs)
725.58 lbs
Total Weight (kg)
329.12 kg
Density Used
8.34 lbs/gal
Volume (Liters)
329.33 L
Formula Used: Weight = 87 gallons × 8.34 lbs/gal (Density)
Weight Comparison Table
| Liquid Type | Volume | Weight (lbs) | Weight (kg) |
|---|
*Assuming constant volume
Visual Weight Comparison
Comparison of selected volume across different liquid densities.
Calculate the Weight of 87 Gallons of Water: A Complete Guide
Whether you are designing a structural support for an aquarium, calculating the load for a transport truck, or simply curious about fluid dynamics, needing to calculate the weight of 87 gallons of water is a common engineering and logistical task. Water is deceptively heavy, and accurate calculations are critical for safety and efficiency.
Quick Answer:
For standard fresh water at room temperature (approx 62°F), 87 gallons weighs approximately 725.58 pounds (329.12 kilograms).
For standard fresh water at room temperature (approx 62°F), 87 gallons weighs approximately 725.58 pounds (329.12 kilograms).
What is the Weight of 87 Gallons of Water?
To accurately calculate the weight of 87 gallons of water, one must understand that "gallon" is a measure of volume, while "pound" is a measure of weight (force). The bridge between these two is density. The standard figure used in the United States for fresh water is 8.34 pounds per gallon.
However, this weight is not a universal constant. It fluctuates based on factors such as temperature, atmospheric pressure, and purity (salinity). For example, 87 gallons of seawater weighs significantly more than 87 gallons of pure distilled water due to the dissolved salts.
The Formula and Mathematical Explanation
The calculation is straightforward but relies on precise variables. The formula to calculate the weight of 87 gallons of water is:
Weight (W) = Volume (V) × Density (D)
Variable Explanations
| Variable | Meaning | Unit (Imperial) | Typical Range |
|---|---|---|---|
| Volume (V) | Amount of space occupied | Gallons (gal) | 0 – ∞ |
| Density (D) | Mass per unit of volume | Pounds per Gallon (lbs/gal) | 8.00 – 8.55 (for water) |
| Weight (W) | Total force exerted by gravity | Pounds (lbs) | Result |
Practical Examples: Real-World Use Cases
Example 1: Residential Aquarium
A homeowner wants to install an 87-gallon fish tank on a second-floor wooden deck. To determine if the deck can hold the weight, they must calculate the weight of 87 gallons of water plus the glass and substrate.
- Input Volume: 87 gallons
- Liquid Type: Fresh Water (Density ~8.34 lbs/gal)
- Calculation: 87 × 8.34 = 725.58 lbs
- Interpretation: The water alone weighs over 700 lbs. Adding glass and gravel could push the total over 1,000 lbs, requiring structural reinforcement.
Example 2: Marine Transport Tank
A logistics company is transporting live seafood in a tank holding 87 gallons of seawater.
- Input Volume: 87 gallons
- Liquid Type: Seawater (Density ~8.55 lbs/gal)
- Calculation: 87 × 8.55 = 743.85 lbs
- Interpretation: Seawater is denser. The load is nearly 20 lbs heavier than fresh water, which affects the vehicle's gross weight rating.
How to Use This Calculator
Our tool is designed to help you calculate the weight of 87 gallons of water (or any other amount) instantly. Follow these steps:
- Enter Volume: Input the number of gallons in the "Volume" field. The default is set to 87.
- Select Liquid Type: Choose the state of the water. Standard fresh water is the default, but you can select "Seawater" or "Boiling Water" to see how density changes weight.
- Review Results: The calculator updates in real-time. Look at the "Total Weight (lbs)" for the primary answer.
- Check Intermediates: Convert to Metric (kg) or Liters instantly using the grid below the main result.
Key Factors That Affect Water Weight Results
When you set out to calculate the weight of 87 gallons of water, consider these six critical factors that influence the final number:
- Temperature: Water is densest at roughly 39.2°F (4°C). As it heats up, it expands and becomes lighter per gallon. Boiling water weighs about 8.00 lbs/gal, roughly 4% lighter than cold water.
- Salinity (Dissolved Solids): Saltwater contains dissolved minerals that increase mass without significantly increasing volume. This makes seawater much heavier than fresh water.
- Suspended Particles: Dirty or muddy water carries soil particles, which can drastically increase density well above 8.34 lbs/gal.
- Isotopes (Heavy Water): While rare in daily use, water containing the deuterium isotope (Heavy Water) is roughly 11% denser than standard water.
- Pressure: Water is nearly incompressible, but at extreme depths (like the ocean floor), density increases slightly due to compression.
- Aeration: Water that is heavily aerated (bubbly) has a lower effective density because air pockets displace liquid volume.
Frequently Asked Questions (FAQ)
1. Does 87 gallons of ice weigh the same as 87 gallons of water?
No. When water freezes, it expands by about 9%. Therefore, 87 gallons of solid ice weighs significantly less than 87 gallons of liquid water (approx. 665 lbs vs 725 lbs), because ice is less dense.
2. What is the exact weight of a gallon of water?
There is no single "exact" weight, but 8.345404 lbs is the standard value used at maximum density (39.2°F). At room temperature (70°F), 8.33 lbs is often cited.
3. How do I calculate the weight of 87 gallons of water in kg?
Multiply the weight in pounds by 0.453592. For 87 gallons: 725.58 lbs × 0.453592 ≈ 329.12 kg.
4. Why does the calculator show different results for seawater?
Seawater contains salt, which increases density to approximately 8.55 lbs/gal (1.025 g/cm³). This extra mass is critical for marine applications.
5. Does altitude affect the weight of water?
Directly, very minimally. However, altitude affects the boiling point of water. At higher altitudes, water boils at lower temperatures, which limits how "hot" (and therefore how light) liquid water can get before turning to steam.
6. Is the US gallon the same as the Imperial gallon?
No. One US gallon ≈ 3.785 liters, while one Imperial (UK) gallon ≈ 4.546 liters. This calculator uses US liquid gallons. An Imperial gallon of water weighs 10 lbs.
7. Can I use this for other liquids like gasoline?
Gasoline is lighter than water (approx 6.1 lbs/gal). If you need to calculate fuel weight, you must use the specific density of gasoline, not water.
8. How much weight does an 87-gallon tank add to a floor?
You must calculate the weight of 87 gallons of water (~726 lbs) plus the weight of the tank itself (often 100+ lbs for glass). The total load is likely over 850 lbs.
Related Tools and Internal Resources
Explore our other engineering and fluid calculators to assist with your projects:
- Water Density Calculator – Determine exact density based on precise temperature inputs.
- Liquid Weight Conversion – Convert between liters, gallons, pounds, and kilograms for various fluids.
- Pool Volume Calculator – Estimate total gallons for swimming pools to calculate chemical needs.
- Aquarium Weight Calculator – Specifically designed for fish tanks, including substrate and glass weight.
- Metric to Imperial Converter – Quick conversions for volume and mass units.
- Specific Gravity Chart – Reference table for the densities of common industrial liquids.