Horizontal Tank Volume Calculator
Operators, tank-gauging techs, and inventory engineers use this to turn a measured liquid level into a volume for a horizontal cylindrical tank. Reach for it when strapping a tank, spot-checking a level transmitter, or estimating inventory between manual gauges.
A horizontal cylinder holds a partial-fill volume that is not linear with level: near empty and near full, a small change in level is a small change in volume, while at the middle a small level change moves a lot of liquid. This calculator uses the circular-segment area times length, then reports gallons, oil barrels, and percent full.
The Calculator
Result
Cylindrical body only; dished or flat heads are not included.
The Formula
With radius R = diameter / 2 and fill height h, the wetted cross-section is a circular segment. Multiplied by the length L, the volume is:
That gives cubic feet. Converting: 1 ft³ = 7.480519 US gallons, and 1 barrel = 42 gallons. Percent full is the segment volume over the full-cylinder volume πR²L.
Worked example. An 8 ft diameter, 20 ft long tank filled to h = 4 ft is exactly half full (h = R = 4 ft). The segment term gives R² · acos(0) - 0 = 16 · (π/2) = 25.13 ft², so V = 20 × 25.13 = 502.7 ft³ = 3,760 gal = 89.5 bbl, at 50% full. That matches half of the full πR²L = 1005 ft³.
Assumptions and Limits
- This computes the straight cylindrical body only. Dished, elliptical, or hemispherical heads add volume the tool does not include; for custody-grade inventory use a strapping table that accounts for the heads.
- The tank is assumed truly horizontal. A tilt shifts the level-to-volume relationship and needs a correction the tool does not apply.
- Use consistent feet for all three inputs. The level must be between 0 and the diameter.
- Results are engineering estimates. Verify against the tank's calibration or strapping table and a reference gauge before using for accounting.
FAQ
Why is my level transmitter not linear with volume?
Because a horizontal cylinder is not a straight-sided box. The cross-section is widest at the centerline, so the same inch of level change moves the most liquid near half full and the least near empty or full. That is exactly the segment relationship above.
Should I include the heads?
For a rough inventory, the body-only figure is often close enough. For a bunker, a custody transfer, or leak detection, use the tank's strapping table, which includes head volume and any internal corrections.
Can I use meters instead of feet?
The geometry is unit-neutral, but this tool's gallon and barrel conversions assume feet. If you enter meters, the percent-full figure is still correct, but the gallon and barrel outputs will not be.
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