Formula and Method for Cylinder Volume in Gallons
Volume of a Cylinder:
V = π × r² × h
r = radius (½ × diameter); h = height or length
A cylinder's volume is the area of its circular cross-section times its height: V = π × r² × h, where r is the radius (half the diameter) and h is the height or length of the cylinder. Because a "gallon" is a unit of volume, this calculator also converts that raw cubic-unit volume into US liquid gallons, UK imperial gallons, and liters — useful for sizing water tanks, propane tanks, drums, pipes, and other cylindrical containers.
How the calculation works
Enter the cylinder's diameter and height (or length, for a tank lying on its side) and choose the unit they're both measured in. The calculator halves the diameter to get the radius, squares it, and multiplies by π and the height to get the raw volume in that unit's cubic form. It then converts every measurement to cubic centimeters internally and applies 1 US gallon = 3.785411784 liters and 1 UK imperial gallon = 4.54609 liters, so the gallon results are correct no matter which unit you picked. Diameter — not radius — is what most people measure with a tape measure across a tank or pipe, so double-check which one you're entering.
Common mistakes
- Diameter vs. radius: measuring across the cylinder gives the diameter. Using that number directly as the radius doubles the calculated volume — always halve the diameter first.
- Mixing units: keep diameter and height in the same unit before calculating; entering one in feet and the other in inches produces a badly wrong volume.
- US vs. UK gallons: a UK imperial gallon is about 20% larger than a US gallon (4.546 L vs 3.785 L) — using the wrong one under- or over-states capacity by roughly a fifth.
- Partial fill vs. full capacity: this formula gives the cylinder's total (100%) capacity. A horizontal tank filled only partway needs a circular-segment formula, not a simple percentage of this number.
Real-world applications
- Sizing water storage tanks, cisterns, rain barrels, and well casings
- Estimating propane, fuel oil, or chemical drum capacity in gallons
- Calculating pipe or pipeline segment volume for flow, dosing, or flush-out planning
- Converting aquarium, silo, or cylindrical planter dimensions into fill volume
Frequently Asked Questions
What is the formula for the volume of a cylinder?
How do I convert cylinder volume to gallons?
Does this calculator give the volume for a horizontal (lying-down) tank?
What is the difference between a US gallon and a UK imperial gallon?
Common Tip Percentages
| Service | Typical Tip Range | Notes |
|---|---|---|
| Restaurant (sit-down) | 15–20% | 20%+ for exceptional service |
| Food delivery | 10–20% | Consider extra for long distances |
| Taxi / rideshare | 10–20% | More for assistance with luggage |
| Hotel housekeeping | $2–5/night | Leave daily, not just at checkout |
| Barber / hair salon | 15–20% | On pre-discount total |
| Pizza delivery | 10–15% or $3–5 minimum | Higher in bad weather |
General Household Budget Ratios (50/30/20 Rule)
| Category | % of Net Income | Examples |
|---|---|---|
| Needs | 50% | Rent, groceries, utilities, insurance |
| Wants | 30% | Dining out, entertainment, hobbies |
| Savings / Debt | 20% | Emergency fund, retirement, extra payments |
Common Measurement Conversions for Everyday Use
| Quantity | US / Imperial | Metric Equivalent |
|---|---|---|
| 1 cup | 8 fl oz | 237 mL |
| 1 pint | 16 fl oz | 473 mL |
| 1 quart | 32 fl oz | 946 mL |
| 1 gallon | 128 fl oz | 3.785 L |
| 1 lb | 16 oz | 453.6 g |
| 1 ft | 12 in | 30.48 cm |