📖 How To Use
How to Use This Horizontal Tank Volume Calculator
Getting the precise capacity of a horizontal cylindrical tank — including partial fills — takes under 60 seconds:
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Measure the internal diameter
The diameter is the distance across the circular end of the tank, measured from the inside. Do not use outside dimensions — wall thickness will overstate the volume. Divide the diameter by 2 to get the radius if your tape only shows radius.
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Measure the internal length
This is the horizontal distance from one internal end face to the other. For tanks with dished or hemispherical heads, measure from the straight cylindrical section only, or use the overall internal length for a close approximation.
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Measure or estimate the fill depth
The fill depth is how high the liquid currently sits, measured vertically from the bottom of the tank's interior. To get the full-tank volume, set this equal to the diameter. The calculator uses the exact circular segment formula — not a linear approximation.
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Choose units per field and click Calculate
Each input has its own unit selector — mix ft, in, cm, m, or mm freely. Results appear instantly in litres, US gallons, UK gallons, cubic metres, and weight.
Tip: For a full-tank reading without measuring the current fluid level, simply enter the diameter value into the Fill Depth field. This sets the depth equal to the full diameter, giving you the complete tank capacity.
📐 The Formula
Horizontal Cylindrical Tank Volume Formula
Unlike a rectangular tank (simple multiplication), a horizontal cylinder requires a circular segment calculation because the cross-sectional area changes non-linearly with fill depth:
Partial Fill Volume = L × [r² × arccos((r − h) / r) − (r − h) × √(2rh − h²)]
Where:
r = radius (diameter ÷ 2)
h = fill depth (measured from bottom)
L = tank length
arccos is in radians
Full Tank Volume = π × r² × L
This calculator converts all inputs to centimetres internally, applies the formula, then converts to every output unit simultaneously — so mixed-unit inputs always produce correct results.
Why the Formula Is Non-Linear
At half-full (h = r), the cross-section is exactly a semicircle — half the full circle area. But at 25% depth, the volume is roughly 19% of full capacity, not 25%. At 75% depth, it's approximately 81%. This non-linearity matters whenever you're gauging a partially filled horizontal tank for inventory, billing, or safety.
Unit Conversion Reference
| Unit | Equals Litres | From Litres |
|---|
| 1 Litre (L) | 1 L | × 1 |
| 1 Cubic Metre (m³) | 1,000 L | ÷ 1,000 |
| 1 US Gallon | 3.785 L | ÷ 3.785 |
| 1 UK Gallon | 4.546 L | ÷ 4.546 |
| 1 Cubic Foot (ft³) | 28.317 L | ÷ 28.317 |
| 1 Cubic Inch (in³) | 0.01639 L | × 61.024 |
Water Weight
1 litre of fresh water = 1 kg (or 2.2046 lbs). The weight shown in results is for the water content only — add your tank shell weight for total structural load calculations.
📏 Reference Data
Common Horizontal Tank Sizes & Volumes
Typical manufactured horizontal cylindrical tanks and their calculated full capacities:
| Capacity | Diameter (cm) | Length (cm) | Full Volume (L) | US Gal | Full Weight |
|---|
| 500 L | 80 | 100 | 503 | 133 | 503 kg |
| 1,000 L | 100 | 128 | 1,005 | 265 | 1,005 kg |
| 2,000 L | 120 | 178 | 2,015 | 532 | 2,015 kg |
| 3,000 L | 140 | 196 | 3,001 | 793 | 3,001 kg |
| 5,000 L | 160 | 250 | 5,027 | 1,328 | 5,027 kg |
| 10,000 L | 200 | 320 | 10,053 | 2,655 | 10,053 kg |
| 20,000 L | 250 | 410 | 20,123 | 5,315 | 20,123 kg |
Note: Actual capacities vary by manufacturer. Always verify against the tank's data plate or specification sheet.
🏭 Use Cases
When to Use a Horizontal Tank Volume Calculator
Fuel and Oil Storage Tanks
Underground petrol and diesel storage tanks are almost always horizontal cylinders. Operators use partial-fill volume calculations to reconcile deliveries, monitor for leaks, and comply with environmental reporting requirements. A 1 cm error in dipstick depth on a 2-metre diameter tank can translate to 40–60 litres discrepancy.
Agricultural and Chemical Tanks
Farmers storing water, fertilisers, or crop protection chemicals in skid-mounted horizontal tanks need accurate fill readings to mix solutions at correct concentrations and avoid over-ordering or running out of supply mid-season.
Compressed Gas and Propane Cylinders
Large horizontal propane and LPG storage vessels follow the same geometry. While gas volume requires additional pressure corrections, the liquid phase volume at the bottom uses the same horizontal cylinder formula — critical for refill scheduling and safety margin calculations.
Industrial Process and Water Treatment
Buffer tanks, sedimentation tanks, and surge vessels in industrial plants are frequently horizontal cylindrical vessels. Process engineers use partial-fill volume to calculate residence times, dosing rates, and pump run-on times.
Road and Rail Tankers
Tank trucks and rail cars carry fuel, chemicals, milk, and food-grade liquids in horizontal cylindrical vessels. Knowing the volume at any given dip measurement is essential for loading, unloading, and customs declarations.
Note: This calculator assumes a standard right-circular cylinder. Tanks with hemispherical or ellipsoidal end caps have slightly larger capacities — add approximately 10–15% for hemispherical heads and check manufacturer specs for exact figures.
❓ FAQ
Frequently Asked Questions
How do I calculate the volume of a horizontal cylindrical tank?
Use the formula: V = L × [r² × arccos((r − h) / r) − (r − h) × √(2rh − h²)], where r is the radius, h is the fill depth, and L is the tank length. For a full tank, this simplifies to V = π × r² × L. This calculator performs all the trigonometry automatically — just enter diameter, length, and fill depth.
Why is the horizontal tank volume formula more complex than for rectangular tanks?
A rectangular tank has the same cross-sectional area at every fill level, so volume increases linearly with depth. In a horizontal cylinder, the cross-sectional area (a circular segment) changes non-linearly with fill height — it's smallest near the bottom and top, and widest at the midpoint. This requires an arccos (inverse cosine) calculation that makes simple arithmetic insufficient.
How do I measure the fill depth of a horizontal tank?
Lower a calibrated dipstick or measuring tape vertically through the tank's top opening until it touches the bottom. The wet mark on the stick when withdrawn shows the liquid depth from the bottom of the tank interior. For safety, always use approved dipsticks for fuel tanks and ensure no ignition sources are nearby.
What is a horizontal tank volume calculator used for?
It is used to determine the liquid volume in storage tanks, fuel tanks, water tanks, chemical vessels, propane tanks, and rail or road tankers at any partial fill level. Key applications include fuel inventory management, chemical dosing, refill scheduling, environmental compliance reporting, and structural load assessment.
Does the calculator account for tanks with dished ends?
This calculator uses the standard straight-cylinder formula, which applies to the cylindrical section of the tank. Tanks with hemispherical end caps hold approximately 10–15% more than the cylindrical calculation shows. For precise results with dished heads, use the manufacturer's strapping table or add the end-cap volume separately (hemisphere volume = (2/3) × π × r³ per head).
How many litres is a horizontal tank that is half full?
Exactly half the full capacity. When fill depth equals the radius (half the diameter), the circular cross-section is exactly a semicircle — which is precisely half the full circle area. So unlike 25% and 75% fill levels, the half-full mark on a horizontal cylinder is exactly 50% of total volume.
Can I use this calculator for diesel, fuel oil, or chemicals instead of water?
Yes — volume results in litres, gallons, and cubic metres apply to any liquid. The weight shown assumes fresh water (1 kg/litre). For other fluids, multiply the litre result by the liquid's density: diesel ≈ 0.85 kg/L, petrol ≈ 0.74 kg/L, propane (liquid) ≈ 0.51 kg/L, sulphuric acid ≈ 1.84 kg/L. Always use the correct density for structural and transport calculations.
How do I convert horizontal tank volume from litres to US gallons?
Divide the litre value by 3.78541 to get US gallons. For example, 1,000 litres ÷ 3.78541 = 264.2 US gallons. This calculator displays both simultaneously so you never need to convert manually. Note that UK/Imperial gallons are larger: 1 UK gallon = 4.54609 litres, so 1,000 litres = 219.97 UK gallons.