Enter diameter (or radius) and height — mix units freely
Diameter input mode
Enter your measurements
Diameter
Height
Fill Level
100%
25%50%75%Full
⚠ Please enter valid values (greater than zero) for both diameter and height.
WaterTankCalculator.com — Cylindrical Tank Results
Your Results
Total Volume
—
Litres (L)
Cubic Metres
— m³
US Gallons
— gal
UK/Imperial Gallons
— gal
Cubic Feet
— ft³
Cubic Inches
— in³
Water Weight
— kg
Weight (lbs)
— lbs
Fill Level
— %
Visual Fill Level
📖 How To Use
How to Use This Cylindrical Tank Volume Calculator
Getting your round tank's exact capacity takes under 30 seconds:
Choose diameter or radius mode
Most tanks are measured across their widest point — that's the diameter. If you only have the radius (half the diameter), switch to Radius mode using the toggle at the top. Both give identical results.
Enter the diameter (or radius)
Measure the internal diameter of your cylindrical tank — the distance across the inside, not the outside. Use whatever unit is on your tape measure: feet, inches, cm, m, or mm.
Enter the height
Measure from the inside bottom up to the overflow or the highest level the water actually reaches — not to the top of the lid. Height can use a different unit from diameter; this calculator converts everything automatically.
Set the fill level (optional)
Drag the slider to calculate volume at a partial fill, e.g. 60% for a partially-filled tank. In an upright cylinder, the percentage of depth and the percentage of volume are the same, so 60% of the height holds 60% of the water. Leave it at 100% for full capacity.
Hit Calculate
Results appear instantly — litres, US and UK gallons, cubic metres, cubic feet, and water weight in kg and lbs. The note under the results shows the working in feet and gallons, plus how many gallons each inch of depth holds. Copy or print them with one click.
Tip: Cylindrical tanks often have a slight taper or domed base. For tapered tanks, use the average internal diameter. For tanks with a cone-shaped bottom, measure the straight-sided height here and add the cone with our Cone Bottom Tank Volume Calculator. A domed (raised) floor takes some volume away, so subtract it.
📐 The Formula
Cylindrical Tank Volume Formula
The volume of a cylinder is calculated using the radius (half the diameter) and the height. The key constant is π (pi ≈ 3.14159):
Volume = π × r² × h
Where: r = radius (half diameter), h = height
Litres (cm inputs): V (L) = π × r² × h ÷ 1,000
Cubic metres (m inputs): V (m³) = π × r² × h
Cubic feet (ft inputs): V (ft³) = π × r² × h
US gallons: ft³ × 7.48, or in³ ÷ 231
This calculator converts all dimensions to centimetres internally before calculating, so mixed-unit inputs (e.g., diameter in inches and height in metres) always produce correct results.
Worked Example
A cylindrical water tank with an internal diameter of 1.2 m and height of 1.5 m:
r = 1.2 ÷ 2 = 0.6 m
V = π × 0.6² × 1.5
V = 3.14159 × 0.36 × 1.5
V = 1.696 m³ = 1,696 litres
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. The exact figure is 0.998 kg per litre at 20 °C (68 °F), so 1 kg per litre is the standard rounding used for load estimates. In US units, 1 cubic foot = 7.48 US gallons and 1 US gallon = 231 cubic inches.
Common manufactured cylindrical tank dimensions and their calculated volumes:
Capacity
Diameter × Height (cm)
Diameter × Height (ft)
Litres
US Gal
Full Weight
250 L
60 × 90
2.0 × 3.0
254
67
254 kg
500 L
75 × 114
2.5 × 3.7
504
133
504 kg
1,000 L
100 × 128
3.3 × 4.2
1,005
266
1,005 kg
1,500 L
120 × 133
3.9 × 4.4
1,504
397
1,504 kg
2,000 L
130 × 151
4.3 × 5.0
2,004
529
2,004 kg
5,000 L
175 × 208
5.7 × 6.8
5,003
1,322
5,003 kg
10,000 L
230 × 241
7.5 × 7.9
10,013
2,645
10,013 kg
Note: Actual manufacturer dimensions vary. Always verify against the supplier's data sheet. Dimensions shown are internal measurements; Full Weight is the water only — add the empty tank's weight.
🏠 Use Cases
When to Use a Cylindrical Tank Volume Calculator
🏠
Rooftop & Overhead Tanks
Most plastic rooftop tanks (HDPE, polyethylene) are cylindrical. Calculate exact capacity to size your household supply correctly.
🏭
Industrial Storage
Vertical cylindrical tanks are the standard for industrial water, fuel, and chemical storage. Verify capacity before filling or ordering.
🌾
Agricultural Use
Round poly tanks on farms and smallholdings need accurate volume to plan irrigation schedules and livestock water requirements.
🚒
Fire & Emergency
Fire water reserves are set by the local fire code or fire authority. Use the calculator to check a tank's actual volume against the reserve you have been given.
💧
Rainwater Harvesting
Cylindrical rainwater tanks need accurate volume estimates to match collection area and seasonal rainfall for reliable off-grid supply.
🔧
Treatment Systems
Correct chlorine dosage and chemical treatment depends on exact volume. Use this calculator before adding any treatment chemicals.
🧮 Worked Example
Worked example: measuring an installed poly tank in feet and inches
You can't reach across a tank that is already installed, so you wrap a tape around it: the circumference is 15 ft 8 in (188 in). The wall is about ¼ in thick, and the overflow sits 66 in above the inside floor.
Outside diameter: 188 ÷ π = 59.84 in. Inside diameter: 59.84 − 2 × 0.25 = 59.34 in.
Volume: π × (59.34 ÷ 2)² × 66 = 182,530 in³.
In gallons: 182,530 ÷ 231 = 790 US gallons (2,991 L, 658 UK gallons).
Per inch of depth: 790 ÷ 66 ≈ 12 gallons — handy for reading the level with a dipstick.
Water weight when full: 790 × 8.34 ≈ 6,590 lb (2,990 kg), plus the tank itself.
Enter 59.34 in and 66 in above to check it. Using the outside diameter instead would add about 13 gallons — under 2% on a thin plastic tank, but much more on concrete.
❓ FAQ
Frequently Asked Questions
How do I calculate the volume of a cylindrical water tank?
Use the formula V = π × r² × h, where r is the radius (half the diameter) and h is the height. With feet, the answer is in cubic feet — multiply by 7.48 for US gallons. With inches, divide the cubic inches by 231. With centimetres, divide the result by 1,000 to get litres. This calculator handles all conversions automatically — just enter diameter (or radius) and height in any unit.
What is the difference between diameter and radius?
The diameter is the full width of the tank measured straight across the centre. The radius is exactly half the diameter — the distance from the centre to the edge. Use whichever you have; this calculator accepts both via the toggle button above the inputs.
Should I use internal or external diameter for the calculation?
Always use the internal diameter. The tank wall thickness (typically 5–15 mm, about ¼–½ in, for polyethylene; 50 mm / 2 in or more for concrete) reduces the usable internal space. Using the external diameter overstates capacity by only about 1–5% on a thin-walled plastic tank, but by 10% or more on a small concrete tank, because the error is doubled across the diameter and then squared.
How heavy is a full cylindrical water tank?
Water weighs about 1 kg per litre, or 8.34 lb per US gallon. A 1,000-litre (264-gallon) cylindrical tank carries about 1,000 kg (2,200 lb) of water plus the tank shell — roughly 20–50 kg for polyethylene, more for fibreglass, steel or concrete. For rooftop installation, always confirm your structure can support the combined load. Use our Water Tank Weight Calculator for detailed load analysis.
How do I measure the diameter of an existing round tank?
For small tanks, place a straight rule or tape measure across the widest part. For larger tanks where measuring across is difficult, measure the circumference (all the way around the outside), then divide by π (3.14159) to get the external diameter, then subtract twice the wall thickness to get the internal diameter. Alternatively, most manufacturers stamp the nominal capacity on the tank — cross-check with this calculator.
Can I use this calculator for horizontal cylindrical tanks?
For a fully horizontal cylinder, this calculator gives the correct total capacity (the math is the same regardless of orientation). However, partial fill calculations are only accurate for vertical tanks — a horizontal tank's cross-section fills non-linearly. For partially-filled horizontal tanks, use our Horizontal Tank Volume Calculator.
How many litres per day does a household need?
It varies a lot by country. WHO guidance links about 50 litres per person per day to an intermediate level of access and 100 litres or more to optimal access. US homes average about 82 gallons (310 L) per person per day including outdoor use (EPA WaterSense), while many European homes use roughly 120–150 L. A family of 4 at 100–200 L each uses 400–800 litres (about 105–210 US gallons) a day, so a 1,000-litre (264-gallon) tank lasts them about 1¼–2½ days.
What size cylindrical tank do I need for a home?
Where the supply is unreliable, a common rule is to store 3–5 days of household water. For a family of 4 using 150 L (40 gallons) per person per day, that's 1,800–3,000 litres (about 475–790 US gallons). A 1,500 L cylindrical tank (approx. 1.2 m diameter × 1.33 m tall) covers 2–3 days at full comfort. Use our Tank Size for Home Calculator for a personalised recommendation.
✅ Sources & Review
Sources and review
The formula is standard geometry; the conversion factors and figures on this page come from these references:
US EPA WaterSense — Statistics and Facts: the average American uses about 82 gallons of water a day at home.
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.
