Vertical Cylinder · Horizontal Cylinder · Rectangular Tank
Tank Volume Calculator
Enter the actual internal tank dimensions and the measured liquid level to calculate filled capacity in litres, cubic metres, and US gallons. Use internal dimensions for final work. Outside plate dimensions can make the result look better on paper while the real usable capacity remains lower.
Internal tank reference. The blue area and fill line update as dimensions change.
Fix the highlighted field above to see the tank volume.
Practical Reference
Tank Shapes and Capacity Basics
Tank capacity looks simple until fabrication details enter the picture. A drawing may show outside dimensions, the fabricator may quote nominal capacity, and the site team may measure liquid from a different reference point. The calculator gives geometric volume from the dimensions entered. For purchase approval or process work, confirm that those dimensions describe the real internal space.
Vertical Cylindrical Tank
A vertical cylinder has a constant circular area from bottom to top when the shell is straight and the ends are flat. Partial volume is therefore easy: the liquid level divided by internal height gives the same proportion of the cylindrical shell volume. This is common for water, chemical, oil, and process tanks installed upright.
Horizontal Cylindrical Tank
A horizontal cylinder needs circular-segment geometry. Half the liquid depth means half the capacity, but one-quarter depth does not mean one-quarter capacity. This matters during tanker calibration, diesel storage checks, underground vessel measurements, and any estimate based on a dip reading.
Rectangular Tank
A rectangular tank uses internal length multiplied by internal width multiplied by liquid depth. The formula is direct, but the input basis still matters. Stiffeners, sloped bottoms, sumps, internal partitions, and lining can reduce usable capacity even when the outer box dimensions look correct.
Internal Dimensions
Capacity belongs to the empty space inside the tank, not the steel envelope outside it. If a fabricated tank is specified by outside diameter, deduct two plate thicknesses to obtain the internal diameter. Do the same for rectangular length, width, and height where the plates sit inside the stated outer dimensions.
Fill Level
Fill level must be measured from the true internal bottom to the liquid surface. A dip from the roof, a gauge zero above the bottom, or a sloped floor can shift the result. Record the reference point on the calibration sheet so the same reading means the same thing during operation.
Gross and Usable Capacity
Gross capacity is the full geometric space. Usable capacity is normally lower because of freeboard, overflow level, suction position, heating coils, agitator parts, dead stock, and operating limits. Keep both figures separate. A tank sold as 10,000 litres may not safely deliver 10,000 usable litres in service.
Calculation Reference
Tank Volume Formulas
Use internal dimensions in one unit system. The calculator converts the final geometric volume into litres, cubic metres, and US gallons. Horizontal partial fill is the only case where the filled percentage is not equal to the level percentage.
- Confirm the tank shape and use actual internal dimensions.Inside size = outside size − plate and lining deductions
- Calculate the full geometric capacity for the selected tank.Vfull = cross-sectional area × internal length or height
- Apply the measured liquid level to calculate the current filled volume.Vfilled = f(shape, dimensions, fill level)
- Vertical CylinderV = π × (D ÷ 2)² × h
- Horizontal CylinderV = L × [r² cos⁻¹((r − h) ÷ r) − (r − h)√(2rh − h²)]
- Rectangular TankV = L × W × h
- Full CylinderVfull = π × (D ÷ 2)² × L or H
- Full RectangularVfull = L × W × H
- D Internal tank diameter
- r Internal radius, equal to D ÷ 2
- L Internal tank length
- W Internal rectangular width
- H Full internal tank height
- h Measured liquid level from the bottom
Worked Example: Half-Full Horizontal Cylinder
- Internal diameter2.000 m
- Internal length4.000 m
- Fill depth1.000 m
- Segment areaπ × 1² ÷ 2 = 1.570796 m²
- Filled volume1.570796 × 4 = 6.283185 m³
Result: 6,283.19 L · 6.283185 m³ · 1,659.07 US gal
For connected pipeline hold-up, use the Pipe Volume Calculator. For shell and plate purchase estimates, use the Steel Weight Calculator.
Frequently Asked Questions
Tank Volume Questions
These answers cover the points that usually cause differences between a quick geometric calculation, a fabrication drawing, and the capacity seen during commissioning.
Should I enter internal or external tank dimensions?
Enter internal dimensions whenever possible. External dimensions include plate thickness, so using them directly overstates capacity. If only outside dimensions are available, deduct the plate thickness from both sides of every relevant dimension before calculating.
How is partial volume calculated in a vertical cylindrical tank?
For a vertical cylinder with flat ends, the liquid cross-section stays constant. The calculator multiplies the circular internal area by the measured fill level, so volume rises directly with liquid height.
Why is a horizontal cylinder harder to calculate when partly full?
A horizontal cylinder does not gain the same volume for every millimetre of level. Near the bottom and top, a small level change adds less volume than the same change near the centre. The calculator uses the circular-segment formula rather than a simple percentage shortcut.
Does the calculator include dished or hemispherical tank ends?
No. The cylindrical calculations use the straight internal length with flat-end geometry. Dished, torispherical, ellipsoidal, conical, or hemispherical ends add or remove volume depending on the construction and must be calculated separately from approved fabrication dimensions.
Does plate thickness reduce the tank capacity?
Yes. A tank made to an outside diameter or outside box size has a smaller internal space after plate thickness is deducted. The difference can become significant on thick pressure vessels, rubber-lined tanks, FRP-lined steel tanks, and small process vessels.
What is dead volume below the suction nozzle?
Dead volume is liquid that remains below the lowest usable outlet or suction point. It may be physically inside the tank but unavailable to the pump or process. Gross geometric capacity and usable operating capacity should therefore be recorded separately.
Are the gallons US gallons or Imperial gallons?
The calculator reports US liquid gallons. One US gallon equals 3.785411784 litres. For Indian drawings, tenders, and site records, litres and cubic metres are usually the clearest primary units.
Does the result include coils, baffles, agitator shafts, or internal piping?
No. The result is the clear geometric volume of the selected tank shape. Internal coils, baffles, agitator parts, dip pipes, supports, linings, and other fittings displace liquid and should be deducted when accurate usable capacity is required.
Buying and Checking Checklist
How to Avoid Tank Fabrication & Capacity Errors in India
Capacity disputes usually start with an unclear drawing or an unverified assumption. The purchase order says a nominal figure, the fabricator works from outside dimensions, and the site team expects every litre to be pumpable. Fix the calculation basis before plate cutting starts.
1. Confirm flat ends or dished ends
A flat-ended cylinder and a vessel with torispherical, ellipsoidal, hemispherical, or conical ends do not have the same capacity. Do not use only shell diameter and overall length when the ends are formed.
Ask for the straight shell length, end type, dish depth, knuckle radius, and approved internal profile. Calculate the end volumes separately or use the fabricator’s approved vessel drawing.
2. Check whether dimensions are inside or outside
Plate thickness takes away internal capacity. A 2,000 mm outside-diameter tank made from 10 mm plate does not have a 2,000 mm internal diameter. The clear diameter is closer to 1,980 mm before considering lining and fabrication tolerance.
The capacity difference grows with diameter squared. For thick vessels or small tanks, this is not a minor drafting detail. Put “ID” or “OD” clearly beside every critical dimension.
3. Deduct lining and internal displacement
Rubber lining, FRP lining, brick lining, coils, agitator shafts, dip pipes, baffles, supports, and internal columns all occupy space. A basic geometric calculation assumes the inside is empty.
For process guarantees, prepare a displacement list from approved drawings and deduct it from gross capacity. Do not wait until water calibration to discover that the operating volume is short.
4. Account for dead volume below the suction nozzle
Liquid below the lowest suction or drain opening may remain trapped. This dead volume cannot be counted as normal usable stock, even though it appears in the gross tank capacity.
Record the suction nozzle centreline, bottom slope, sump geometry, minimum pump submergence, and drain arrangement. State gross, working, and usable capacity as separate figures.
5. Protect the freeboard and overflow allowance
A tank should not normally operate filled to the roof. Thermal expansion, foaming, agitation, wave action, inlet surges, and level-control delay need free space. The safe working capacity is therefore lower than the full geometric result.
Confirm the high-level alarm, overflow nozzle, venting basis, and operating maximum. A larger printed capacity is not useful when the process cannot safely use it.
6. Calibrate after fabrication and installation
Rolling tolerance, weld shrinkage, floor slope, foundation settlement, and field modification can shift the final capacity. For custody, batching, chemical dosing, or inventory control, calculation alone may not be enough.
Use a controlled water-fill calibration or an approved level-to-volume table where accuracy matters. Keep the final calibration record with the tank drawing, nozzle schedule, and instrument range.
Simple approval routine
Confirm the internal dimensions, end geometry, plate and lining deductions, nozzle elevations, freeboard, and internal displacement. Calculate gross capacity first, usable capacity second, and then verify the result during commissioning. This avoids the common situation where a tank is technically complete but still fails the process requirement.