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Horizontal Tank Volume Calculator — Partial Fill from Depth

Calculate Liquid Volume in Horizontal Cylindrical Tanks with Flat, Dished, or Elliptical Heads

Free horizontal tank volume calculator for plant operators, field engineers, and fuel handlers. Enter the tank diameter, tank length, and current liquid depth to calculate the volume of liquid in a horizontal cylindrical tank at any fill level. Supports flat, standard dished (ASME flanged & dished), 2:1 elliptical, and hemispherical head types.

Unlike a simple cylinder calculator, this tool handles the geometry of partially filled horizontal cylinders using the exact circular segment integral. Essential for accurate inventory measurements on fuel tanks, process vessels, chemical storage tanks, and water tanks where you are dipping the tank with a gauge stick and need the actual volume, not a linear estimate.

Pro Tip: A horizontal tank is not linear: 50% depth is not 50% volume. At the bottom third of the tank, each inch of depth holds less volume than at the middle. This means your gauge stick over-reports how much fuel you have at low levels and under-reports at high levels. Always use the actual circular segment calculation, not a linear interpolation, for inventory accuracy.

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Start Using This Tool See How It Works

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Horizontal Tank Volume Calculator
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How It Works

  1. Enter Tank Dimensions

    Measure the inside diameter (ID) and the straight shell length (cylinder length, excluding heads) of the tank. Use inches or feet and the calculator converts internally. If you only have the outside diameter, subtract twice the wall thickness.

  2. Select Head Type

    Choose flat (no head volume), ASME flanged and dished (standard dished), 2:1 semi-elliptical, or hemispherical. The head type affects the total tank volume and the partial fill volume at any depth. Most fuel storage tanks use flat or dished heads. Most ASME pressure vessels use 2:1 elliptical or hemispherical heads.

  3. Enter Current Liquid Depth

    Measure the liquid depth from the inside bottom of the tank to the liquid surface using a gauge stick, sight glass, or level transmitter. Enter this value in the same units as your tank dimensions. The calculator computes the corresponding volume using the exact circular segment formula plus the head contribution.

  4. Review Volume Results

    The calculator outputs current liquid volume in gallons, barrels, cubic feet, and liters. It also shows the total tank capacity, percentage full, and the ullage (empty space above the liquid). Use percent full for inventory reporting and ullage for fill-stop calculations.

  5. Generate a Strapping Table (Optional)

    Export a strapping table that shows volume at each inch of depth for the full tank height. Post this table at the tank gauge point for quick field readings without pulling out a calculator every time you dip the tank.

Built For

  • Fuel distributors calculating inventory in horizontal above-ground storage tanks during delivery scheduling
  • Plant operators measuring product volume in horizontal process vessels during batch operations
  • Farm operators checking diesel and gasoline tank levels for fuel management and reorder planning
  • Environmental compliance staff verifying tank inventory for SPCC plan reporting and leak detection
  • Chemical plant operators calculating chemical inventory in horizontal storage tanks for process control
  • Fire departments estimating remaining water volume in horizontal water tankers during emergency response
  • Tank truck drivers verifying load volume against bill of lading using tank dimensions and stick measurement

Features & Capabilities

Exact Circular Segment Calculation

Uses the definite integral of the circular segment area, not a linear approximation. At low and high fill levels, the non-linear relationship between depth and volume is significant. A 10% error in volume at the bottom of a 10,000-gallon tank is 1,000 gallons of fuel.

Four Head Types

Supports flat heads (no additional volume), ASME flanged and dished (approximately 1.06x straight shell volume contribution), 2:1 semi-elliptical (standard for pressure vessels), and hemispherical (maximum volume per head). Each head type uses the correct partial volume formula at any fill level.

Strapping Table Generator

Generate a complete strapping table showing volume at every inch (or centimeter) of depth from empty to full. Post this at your tank for quick manual readings. Export as PDF or CSV for tank records.

Multiple Unit Output

Returns volume in US gallons, imperial gallons, barrels (42 US gal), cubic feet, cubic meters, and liters. No separate unit conversion needed for inventory reporting in different systems.

Ullage Calculation

Shows the empty space (ullage) above the liquid surface. Essential for determining how much product can be added before the tank is full. Ullage is the standard measurement for tanker loading operations.

PDF Export

Export your tank calculation and strapping table as a branded PDF for tank records, SPCC documentation, or delivery verification.

Frequently Asked Questions

Because the cross-section is a circle, not a rectangle. At the bottom and top of the tank, each inch of depth corresponds to a narrow sliver of area. At the middle, each inch corresponds to the widest part of the circle. The volume per inch of depth varies by a factor of 3-4x from the bottom to the center. Using a linear estimate (depth/diameter x total volume) introduces up to 20% error at partial fill levels.
Most standard horizontal above-ground storage tanks (ASTs) for fuel use flat heads or standard dished (ASME flanged and dished) heads. ASME pressure vessels typically use 2:1 semi-elliptical heads. If you are unsure, check the tank nameplate or data sheet. For flat-head approximations on dished-head tanks, the error is typically under 3% of total volume.
Use a clean, straight gauge stick (dip stick) lowered vertically to the tank bottom. Read the wet line where the liquid level shows on the stick. For fuel, apply paste to the stick that changes color on contact with the specific fuel type. For dark liquids, use a plumb bob on a graduated tape. Electronic level transmitters (pressure, ultrasonic, or radar) provide continuous readings without manual dipping.
Vertical cylindrical tanks are much simpler: volume is linear with depth. V = pi x (D/2)^2 x h. This calculator is specifically designed for horizontal tanks where the partial-fill geometry is non-linear. For vertical tanks, a simple cylinder formula is all you need.

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