🚰 Water Tank Calculator PRO
Capacity, water volume, weight, and cost for 4 tank shapes.
Tank + Water Level — updates as you type
Storage vessel with water volume. Capacity follows length, width and water depth.
1 Tank Shape
2 Dimensions
3 Cost & Details
Client Details
Results
Capacity
Water Volume
Weight
Water Tank Sizing Guide
Show formulas & tips ▼
Volume Formulas
Rectangular: V = L × W × H
Cylindrical:V = π × r² × H (r = diameter ÷ 2)
Hemispherical: V = (2/3) × π × r³
Capsule: V = π × r² × (H − 2r) + (4/3) × π × r³
Conversions
1 cubic foot = 7.48 US gallons = 28.32 liters
1 US gallon = 3.785 liters = 8.34 lb (water weight)
1 liter = 1 kg (water) = 2.205 lb
Tank Material Weight
| Material | Density (kg/m³) |
|---|---|
| Steel | 7,850 |
| Stainless Steel | 8,000 |
| Plastic (HDPE) | 950 |
| Concrete | 2,400 |
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Whether you are sizing a water storage tank, calculating the fill time for a pool, determining chemical dosing rates for a treatment system, or estimating the weight of a full tank for structural design, accurate volume and weight calculations are essential. Our tank calculator computes volume, weight, fill time, and chemical dosing for cylindrical and rectangular tanks of any dimension. Enter the tank diameter and height (for cylinders) or length, width, and height (for rectangles), and get back the volume in gallons, liters, and cubic feet, plus the weight in pounds and kilograms.
Tank volume calculations follow basic geometric formulas. For a cylindrical tank: Volume = PI x radius squared x height. A 4-foot-diameter, 8-foot-tall cylindrical tank holds approximately 753 gallons (PI x 2^2 x 8 x 7.48 = 753 gallons, where 7.48 is the conversion factor from cubic feet to gallons). For a rectangular tank: Volume = length x width x height. A 4x4x8-foot rectangular tank holds approximately 957 gallons (4 x 4 x 8 x 7.48 = 957 gallons). The calculator handles both shapes and displays results in gallons, liters, cubic feet, and cubic meters.
Water weight is straightforward: one gallon of water weighs 8.34 pounds (1 kilogram per liter). A full 753-gallon cylindrical tank weighs 6,280 pounds of water alone (753 x 8.34), plus the tank weight itself. Steel tanks weigh approximately 50 to 100 pounds per 100 gallons of capacity. Polyethylene tanks weigh approximately 15 to 30 pounds per 100 gallons. The calculator adds the estimated tank weight based on material type, giving you the total filled weight for structural design.
Fill time depends on the incoming flow rate. A standard residential water supply delivers 5 to 10 gallons per minute (GPM). Filling a 753-gallon tank at 8 GPM takes approximately 94 minutes (753 / 8 = 94). A fire hydrant delivers 500 to 1,500 GPM, filling the same tank in less than 2 minutes. The calculator accepts flow rate in GPM, liters per minute, or cubic feet per second and displays the fill time in hours, minutes, and seconds.
Chemical dosing calculations are used for water treatment, pool maintenance, and agricultural applications. For pool chlorination, the standard dose is 1 to 3 pounds of chlorine per 10,000 gallons. For a 15,000-gallon pool requiring a 2 ppm (parts per million) increase: dose = (Volume in gallons x Desired increase in ppm) / 1,000,000 x 8.34. For 15,000 gallons and 2 ppm: dose = (15,000 x 2) / 1,000,000 x 8.34 = 0.25 pounds of chlorine. The calculator performs these dosing calculations for common treatment chemicals.
📖 How to Use the Tank Calculator
Select Tank Shape
Choose cylindrical (round) or rectangular (square/rectangle) tank shape. The calculator uses different volume formulas for each shape.
Enter Tank Dimensions
For cylindrical tanks, enter the diameter and height (or length) in feet and inches. For rectangular tanks, enter the length, width, and height. Use the inside dimensions for accurate volume.
Choose Measurement Units
Select feet/inches or meters/centimeters. The calculator displays results in gallons, liters, cubic feet, and cubic meters automatically.
Select Tank Material
Choose steel, plastic (polyethylene), fiberglass, or concrete. Each material has a different weight per unit volume, which affects the total filled weight.
Enter Flow Rate (Optional)
For fill time calculations, enter the incoming flow rate in gallons per minute (GPM), liters per minute, or cubic feet per second. The calculator computes fill time from empty to full.
Review Results
The calculator displays volume (gallons, liters, cubic feet), empty weight, filled weight, fill time, and chemical dosing rates. Use these values for structural design, procurement, and operation planning.
📐 Tank Volume & Weight Formulas
Tank calculations are based on geometric volume formulas and material density. Here are the key formulas:
Cylindrical Tank Volume: Volume = PI x (Diameter/2)^2 x Height. All dimensions in feet, result in cubic feet. Convert to gallons: Gallons = Cubic Feet x 7.48. For a 4-foot-diameter, 8-foot-tall tank: Volume = PI x 2^2 x 8 = 100.53 cubic feet = 752.9 gallons. Convert to liters: Gallons x 3.785 = 2,850 liters.
Rectangular Tank Volume: Volume = Length x Width x Height. All dimensions in feet, result in cubic feet. For a 4x4x8-foot tank: Volume = 4 x 4 x 8 = 128 cubic feet = 957.4 gallons = 3,624 liters.
Tank Weight (Empty): Depends on material and wall thickness. Empty Weight = Surface Area x Material Thickness x Material Density. For a steel cylinder: steel weighs approximately 490 pounds per cubic foot. A 4-foot-diameter, 8-foot-tall cylinder with 1/8-inch walls: surface area = PI x 4 x 8 = 100.5 square feet. Wall volume = 100.5 x (1/8/12) = 1.05 cubic feet. Weight = 1.05 x 490 = 514 pounds. The calculator uses simplified weight-per-gallon ratios for common tank materials.
Total Filled Weight: Filled Weight = Empty Weight + (Volume x Water Weight Per Gallon). Water weighs 8.34 pounds per gallon. For our 753-gallon tank: Filled Weight = 514 + (753 x 8.34) = 514 + 6,280 = 6,794 pounds. This is the total weight the foundation and supports must carry.
Fill Time: Time = Volume / Flow Rate. For 753 gallons at 8 GPM: 753 / 8 = 94.1 minutes = 1 hour 34 minutes. For 753 gallons at 500 GPM (fire hydrant): 753 / 500 = 1.5 minutes.
Chemical Dosing: Dose (lbs) = (Volume in gallons x Desired ppm) / 1,000,000 x 8.34. For 753 gallons with a 2 ppm target: (753 x 2) / 1,000,000 x 8.34 = 0.0125 pounds = 0.2 ounces. The calculator supports chlorine, calcium hypochlorite, sodium hypochlorite, muriatic acid, and other common treatment chemicals.
⚠️ Common Tank Calculation Mistakes
Using outside dimensions instead of inside dimensions
✓ Tank volume should be calculated using inside dimensions. The wall thickness of steel, plastic, or concrete tanks reduces the internal volume. A tank with 4-foot outside diameter and 1/8-inch walls has an inside diameter of 3.979 feet, reducing volume by approximately 1 percent.
Forgetting to convert units
✓ Volume formulas produce cubic feet, which must be converted to gallons (multiply by 7.48) or liters (multiply by 28.32). Entering dimensions in inches and expecting gallons without conversion produces incorrect results.
Ignoring tank weight
✓ The total filled weight includes the water weight plus the tank weight. A 753-gallon steel tank weighs approximately 6,800 pounds when full, not 6,280 pounds (water only). Structural supports must carry the total filled weight, not just the water weight.
Not accounting for tank shape in cylindrical tanks
✓ A cylindrical tank lying on its side (horizontal) has a different volume-to-height relationship than a vertical cylinder. The calculator provides both orientations - verify which orientation your tank uses.
Using wrong flow rate units
✓ Flow rates are measured in gallons per minute (GPM), liters per minute (LPM), or cubic feet per second (CFS). Mixing units (for example, entering LPM when the calculator expects GPM) produces incorrect fill times.
Not accounting for headspace
✓ Tanks should not be filled to 100 percent capacity. Leave 2 to 5 percent headspace for thermal expansion, foam, and operational flexibility. A 753-gallon tank should be filled to approximately 715 to 738 gallons maximum.
Ignoring chemical concentration
✓ Chemical dosing calculations assume a specific concentration (for example, 12.5 percent sodium hypochlorite for liquid chlorine). Using a different concentration changes the dose. Always verify the concentration of the chemical you are using.
💡 Pro Tips for Tank Sizing & Installation
Size the tank for 24 to 48 hours of supply at peak demand. For a household using 300 gallons per day, a 300 to 600-gallon storage tank provides adequate buffer for power outages and peak usage periods.
Place the tank on a level, reinforced concrete pad that can support the total filled weight. A 753-gallon steel tank weighs approximately 6,800 pounds when full. The pad should extend at least 6 inches beyond the tank on all sides.
Install a level gauge or sight glass to monitor tank contents without opening the tank. Simple float gauges cost $20 to $50 and provide continuous level indication. Electronic level sensors with remote monitoring cost $100 to $500.
Install a pressure relief valve on any pressurized tank. Water expands when heated, and a sealed tank without a relief valve can rupture catastrophically. The relief valve should be rated for the tank's maximum working pressure.
Insulate water storage tanks in freezing climates. A 753-gallon tank with 2-inch fiberglass insulation and a 100-watt thermostatic heater maintains water above 40 degrees F in temperatures down to -20 degrees F. uninsulated tanks in freezing climates will crack and leak.
Support horizontal tanks on saddles that distribute the load across the tank shell. Saddle spacing should be no more than one-third of the tank length from each end. Point loads from narrow supports can deform the tank shell and cause failure.
Mark the tank with its capacity, material, maximum fill level, and date of installation. This information is critical for maintenance, chemical dosing, and structural assessments. Use permanent marker or engraved metal tags.
❓ Tank Calculator - Frequently Asked Questions
A cylindrical tank with 4-foot diameter and 8-foot height holds approximately 753 gallons (100.53 cubic feet). A rectangular tank with 4x4x8-foot dimensions holds approximately 957 gallons (128 cubic feet). The calculator provides exact values based on your dimensions.
Water weighs 8.34 pounds per gallon. A 753-gallon tank weighs 6,280 pounds of water, plus the tank weight (50-100 pounds for steel, 15-30 pounds for plastic). Total filled weight is approximately 6,350 to 6,400 pounds for a steel tank, or 6,300 to 6,320 pounds for a plastic tank.
At a standard residential flow rate of 8 GPM, a 500-gallon tank fills in approximately 63 minutes (500 / 8 = 62.5). At 5 GPM (low pressure): 100 minutes. At 50 GPM (commercial pump): 10 minutes. Enter your specific flow rate for an accurate fill time.
For chlorine dosing: Dose (lbs) = (Volume in gallons x Desired ppm) / 1,000,000 x 8.34. For a 500-gallon tank with 2 ppm target: (500 x 2) / 1,000,000 x 8.34 = 0.0083 lbs = 0.13 oz. The calculator performs this automatically for common chemicals.
A horizontal cylinder has a different volume-to-height relationship than a vertical cylinder. For a horizontal tank, the volume depends on the fill height as a percentage of the diameter, which follows a complex geometric formula. The calculator handles both orientations.
Yes. The calculator provides volume in gallons, liters, and cubic feet for any liquid. Propane weighs approximately 4.2 pounds per gallon; fuel oil weighs approximately 7.1 pounds per gallon. Enter the liquid density for accurate weight calculations. Standard propane tank sizes are 100, 250, 500, and 1,000 gallons.
🏗️ Real-World Tank Projects & Applications
Residential Water Storage Tank: A 500-gallon polyethylene water storage tank measures approximately 46 inches in diameter by 72 inches tall (3.83 x 6 feet). Volume: 500 gallons (1,893 liters). Empty weight: approximately 75 pounds. Filled weight: 500 x 8.34 + 75 = 4,245 pounds. At 8 GPM fill rate: 63 minutes. Material cost: $400 to $600 for a standard poly tank. Installation on a concrete pad: $200 to $400. Total installed cost: $600 to $1,000.
Agricultural Chemical Tank (1,000 gallons): A 1,000-gallon cylindrical steel chemical tank measures approximately 48 inches in diameter by 78 inches tall (4 x 6.5 feet). Volume: 1,000 gallons (3,785 liters). Empty weight: approximately 350 pounds. Filled weight: 1,000 x 8.34 + 350 = 8,690 pounds. Chemical dosing for a 10 ppm chlorine treatment: (1,000 x 10) / 1,000,000 x 8.34 = 0.083 pounds = 1.33 ounces of sodium hypochlorite (12.5% solution). Tank cost: $800 to $1,200. Chemical metering pump: $200 to $500. Total system cost: $1,000 to $1,700.
Commercial Fuel Oil Tank (4,000 gallons): A 4,000-gallon horizontal cylindrical steel tank measures 48 inches in diameter by 20 feet long (4 x 20 feet). Volume: 4,000 gallons (15,140 liters). Empty weight: approximately 2,800 pounds. Filled weight (fuel oil at 7.1 lbs/gal): 4,000 x 7.1 + 2,800 = 31,200 pounds (15.6 tons). Fill time at 50 GPM: 80 minutes. Foundation requirement: reinforced concrete pad capable of supporting 16 tons distributed over the tank footprint. Tank cost: $3,000 to $5,000. Installation with piping, gauges, and containment: $3,000 to $6,000. Total installed cost: $6,000 to $11,000.
Our tank calculator computes volume, weight, fill time, and chemical dosing for cylindrical and rectangular tanks of any dimension. Enter your tank dimensions and material to receive exact volume in gallons, liters, and cubic feet, plus total filled weight and fill time based on your flow rate. The calculator supports both horizontal and vertical cylindrical tanks and performs chemical dosing calculations for water treatment applications. Pair it with our HVAC calculator for mechanical room sizing and our insulation calculator for tank insulation requirements.
✅Method, Sources & Review
Maintained by theBuildingCalc methods desk· Last reviewedSeptember 23, 2026. This calculator implements the standards and references below; every figure can be rechecked against the formulas and worked example on this page.
Results are estimates, not engineering advice. Verify against local codes and licensed professionals for structural, electrical, and gas work. See ourTerms. Spotted an error? Report it— corrections ship with the next review.