Tank Volume Calculator
Enter tank shape and dimensions to compute capacity in gallons, liters, and cubic feet. Supports vertical/horizontal cylinders, rectangular boxes, and oval tanks. Useful for water storage, fuel tanks, and aquariums.
Tank volume calculations show up in dozens of practical applications: sizing rainwater catchment systems, calculating fuel oil for heating, determining aquarium chemical doses, planning septic tanks, and estimating water storage capacity. The math is straightforward but depends on shape — cylinders use πr²h, rectangles use length × width × height, and oval (capsule) tanks combine the two.
This calculator returns total tank capacity in gallons, liters, and cubic feet for the three most common tank shapes. Enter dimensions in inches; the math handles unit conversions. The key conversion: 1 cubic inch = 0.004329 US gallons, or equivalently, 1 US gallon = 231 cubic inches.
For aquariums, hot tubs, and pools specifically, the volume calculation determines chemical dosing accuracy. For fuel and water storage, it tells you operating capacity. For septic and rainwater systems, it determines treatment or supply capacity. For all applications: knowing the volume is essential for any operational or maintenance decision.
Inputs
Height for vertical cylinder; length for horizontal
Results
US Gallons
94.0
Liters
355.8
Cubic Feet
12.57
Water Weight
784 lbs
Tank Details
| Measurement | Value |
|---|---|
| Tank Shape | Cylinder |
| Volume (cubic inches) | 21,714.7 |
| Volume (cubic feet) | 12.57 |
| Capacity (US gallons) | 94.0 |
| Capacity (liters) | 355.8 |
| Water Weight (full) | 784.0 lbs |
Formula
How to use this calculator
- Select tank shape (cylinder, rectangular, or oval).
- Enter dimensions in inches.
- For cylinder: enter height (vertical) or length (horizontal) and diameter.
- For rectangular: enter length, width, and depth.
- For oval: enter total length and width.
- Calculator returns volume in gallons, liters, and cubic feet.
Worked examples
Residential water heater
**Scenario:** Cylindrical water heater 60" tall × 24" diameter. **Calculation:** Volume: π × 12² × 60 = 27,143 cubic inches. Gallons: 27,143 / 231 = 117.5 gallons. **Result:** ~118 gallons capacity. Standard residential water heaters are 30-80 gallons; 100+ gallon tanks indicate large household, commercial use, or boiler integration. Actual usable capacity is slightly less (~85% of total) due to baffles and cold inlet location.
Above-ground oil tank
**Scenario:** Rectangular heating oil tank 60" × 27" × 44" deep (standard "275 gallon"). **Calculation:** Volume: 60 × 27 × 44 = 71,280 cubic inches. Gallons: 71,280 / 231 = 308.5 gallons. **Result:** ~308 actual gallons capacity (the "275 gallon" nominal name refers to usable capacity considering venting and overflow). Oil weighs ~7.2 lbs/gallon, so full tank weighs ~2220 lbs + tank weight. Must be on solid foundation and inspected for leaks regularly.
Large aquarium
**Scenario:** Rectangular aquarium 60" long × 18" deep × 24" tall. **Calculation:** Volume: 60 × 18 × 24 = 25,920 cubic inches. Gallons: 25,920 / 231 = 112.2 gallons. **Result:** ~112 gallons. After substrate (1-2"), decor, and water level, actual water volume is ~95-100 gallons. Allows comfortable space for medium community fish, smaller cichlids, or starter reef tank. Requires sturdy stand and significant equipment.
When to use this calculator
**Calculate tank volume for:**
- **Sizing new tanks**: choosing the right tank for capacity needs. - **Determining contents weight**: weight of water/fuel/liquid. - **Chemical dosing**: aquarium, pool, septic treatment per gallon. - **Filling time estimates**: gallons per minute flow rates. - **Maintenance planning**: volume-based service intervals. - **Insurance and legal**: documenting tank size for permits.
**Tank shape selection:**
- **Cylindrical (vertical)**: most common for water heaters, propane tanks; efficient use of space. - **Cylindrical (horizontal)**: heating oil tanks, fuel storage; better for prone installation. - **Rectangular**: aquariums, custom storage; maximizes space in corners. - **Oval/capsule**: propane tanks (typical for above-ground); pressure resistance.
**Tank material considerations:**
- **Steel (galvanized)**: heating oil, water storage; corrodes over time. - **Polyethylene plastic**: water storage, agriculture; lightweight, durable. - **Fiberglass**: durable, lighter than steel, more expensive. - **Concrete**: septic, large water cisterns; permanent installation. - **Glass**: aquariums; brittle, must be supported.
**Installation considerations:**
- **Indoor vs outdoor**: temperature, sun exposure, safety. - **Above-ground vs buried**: cost, accessibility, freezing risk. - **Foundation**: level base, weight support. - **Ventilation**: required for closed liquid tanks. - **Spill containment**: secondary containment for hazardous liquids.
**Septic system considerations:**
- **Tank size**: based on bedrooms (more = larger). - **Tank type**: concrete, fiberglass, polyethylene. - **Pumping frequency**: every 3-5 years residential. - **Drain field size**: based on tank size and soil percolation. - **Annual inspection**: visual check for damage or backup.
**Heating oil tank considerations:**
- **Above-ground vs underground**: cost vs aesthetics. - **Insurance**: above-ground often cheaper. - **Replacement**: 20-30 year lifespan typical. - **Leak detection**: required by many jurisdictions. - **Filling and gauging**: clear access for delivery trucks.
**Water storage considerations:**
- **Potable vs non-potable**: different regulations. - **Rainwater collection**: requires filtration for non-potable use. - **Pressure vs gravity**: pressure tanks need pump, gravity tanks need elevation. - **Temperature**: prevent freezing in cold climates. - **Microbial control**: closed system prevents bacterial growth.
**Aquarium volume considerations:**
- **Water volume**: net of substrate, decor, fish, plants. - **Chemical treatments**: dose per actual water volume. - **Filtration**: pump GPH should equal 4-10× tank volume. - **Heater wattage**: 5-7W per gallon for tropical. - **Lighting**: depends on plants and fish.
**Conversion between units:**
- 1 US gallon = 3.785 liters = 0.1337 cu ft. - 1 cubic foot = 7.481 gallons = 28.32 liters. - 1 cubic meter = 1000 liters = 264.2 US gallons. - 1 barrel (oil) = 42 US gallons = 158.99 liters.
**Practical tips:**
- **Round down**: actual usable capacity is less than calculated (baffles, overflow, etc.). - **Allow for venting**: tanks need air space and overflow protection. - **Consider thermal expansion**: hot liquids expand; leave headspace. - **Document tank dimensions**: useful for insurance, maintenance. - **Mark fill levels**: helps with operational monitoring.
**Cost considerations:**
- **Plastic water tank** (300 gal): $300-700. - **Steel heating oil tank** (275 gal): $1500-3000 installed. - **Fiberglass septic tank** (1500 gal): $1500-2500 installed (plus excavation, drain field). - **Concrete septic tank** (1500 gal): $1000-2000 installed. - **Large rainwater cistern**: $2000-15000+ depending on size and material.
Common mistakes to avoid
- Confusing diameter and radius. Radius is half of diameter.
- Using English vs metric without conversion. Inches × cubic inches; meters × cubic meters.
- Forgetting unit conversion. 231 cubic inches per US gallon; 3.785 liters per gallon.
- Ignoring actual usable capacity. Tanks have less actual capacity than physical volume.
- Wrong calculation for shape. Cylinder uses πr²h; rectangle uses LWD.
- Forgetting to convert all units to same. Inches throughout, or all feet, or all meters.
- Skipping foundation/installation considerations. Tanks need structure to support full weight.