Enter your horizontal cylinder's diameter, length, and current fluid depth — get exact capacity in litres, gallons, cubic metres, and more. Handles partial fills precisely.
Enter diameter, length, and fill depth — units can differ per field
Enter your tank measurements
Diameter
Length
Fill Depth
⚠ Please enter valid numbers (greater than zero) for all fields. Fill depth must not exceed the diameter.
WaterTankCalculator.com — Horizontal Tank Results
Your Results
Partial Fill Volume
—
Litres (L)
Full Tank (L)
— L
Cubic Metres
— m³
US Gallons
— gal
UK/Imperial Gal
— gal
Cubic Feet
— ft³
Water Weight
— kg
Weight (lbs)
— lbs
% Full
— %
Cross-Section Fill Level
📖 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:
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.
Measure the internal length
This is the horizontal distance from one internal end face to the other. For tanks with flat ends that is all you need. For dished or hemispherical heads, measure the straight cylindrical section only and add the heads separately (see the FAQ below), or use the capsule tank calculator for hemispherical ends — using the overall length overstates the volume.
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 — the reading on a dipstick. To get the full-tank volume, set this equal to the diameter. The calculator uses the exact circular segment formula — not a linear approximation — and the note under the results shows how many gallons one more inch of depth adds at that level.
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:
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 only about 19.6% of full capacity, not 25%; at 10% depth it is just 5.2%. At 75% depth it's about 80.4%, and at 90% depth 94.8%. 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 weighs about 1 kg (2.2046 lb), and 1 US gallon about 8.34 lb (0.998 kg per litre at 20 °C / 68 °F). The weight shown in results is for the water content only — add your tank shell weight for total structural load calculations. In US units, 1 cubic foot = 7.48 US gallons and 1 US gallon = 231 cubic inches.
📏 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
266
1,005 kg
2,000 L
120
178
2,013
532
2,013 kg
3,000 L
140
196
3,017
797
3,017 kg
5,000 L
160
250
5,027
1,328
5,027 kg
10,000 L
200
320
10,053
2,656
10,053 kg
20,000 L
250
410
20,126
5,317
20,126 kg
Note: Actual capacities vary by manufacturer. Always verify against the tank's data plate or specification sheet. In the US, a common 1,000-gallon horizontal tank is about 48 in (122 cm) in diameter and 10 ft 8 in (325 cm) long.
🏭 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. Near the middle of a 2-metre (6.6 ft) diameter, 3.2-metre long tank (about 10,000 L), each centimetre of depth is worth about 64 litres — roughly 43 US gallons per inch — so a small dipstick error matters.
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 cylinder with flat ends. Domed ends add volume beyond the straight section: two hemispherical heads add a whole sphere, (4/3)πr³ — about 17% more on a tank four times as long as its diameter — and common 2:1 ellipsoidal heads add half that. Check the manufacturer's capacity chart for exact figures.
🧮 Worked Example
Worked example: dipping a 1,000-gallon horizontal tank
A flat-ended horizontal tank is 48 in across inside and 128 in long. The dipstick shows 18 in of water.
Full capacity: π × 24² × 128 = 231,623 in³ ÷ 231 = 1,003 US gallons (3,796 L).
At 18 in: r = 24, h = 18, so the segment area = 24² × arccos(6 ÷ 24) − 6 × √(2 × 24 × 18 − 18²) = 759.2 − 139.4 = 619.8 in².
Volume: 619.8 × 128 = 79,336 in³ ÷ 231 = 343 US gallons (1,300 L) — 34% of capacity, even though the depth is 37.5% of the diameter.
The next inch adds about 26 gallons at this level, versus about 8 gallons per inch near the bottom.
Enter 48 in, 128 in and 18 in above to check the 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 — ideally at the middle of the tank, so a slight tilt matters less — 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. Two hemispherical end caps add a whole sphere, (4/3) × π × r³ — about 17% more than the straight section for a tank four times as long as its diameter, and more for shorter tanks. A 2:1 ellipsoidal head adds half a hemisphere, (1/3) × π × r³ per head. For precise results with dished heads, use the manufacturer's strapping (calibration) table, or the capsule tank calculator for hemispherical ends.
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% depth (19.6% and 80.4% of the volume), the half-depth mark on a horizontal cylinder is exactly 50% of total volume — for example, about 501 gallons in a 1,000-gallon tank 48 in across.
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.
✅ Sources & Review
Sources and review
The partial-fill formula is standard circular-segment geometry; the conversion factors and figures on this page come from these references:
USGS Water Science School — Water Density: about 1 kg per litre (62.4 lb/ft³, 8.34 lb per US gallon).
Reviewed by John Mac, PE, Water Systems Specialist
Texas-licensed Professional Engineer with 13+ years in residential water storage and 180+ tank projects. John writes and reviews every calculator on this site.
