Tank Volume Calculator

A tank volume calculator answers one question precisely: how many gallons does this tank actually hold? Enter the tank's shape and dimensions, and the tool computes full capacity in gallons, liters, cubic feet, and cubic meters. Add a dipstick reading and it also tells you how much fuel is sitting in the tank right now, both as gallons and as a percent of capacity.

Property owners can use it to identify a mystery tank before a sale. Fuel oil customers can use it to decide whether there is room for a full delivery. Facility managers can use it to check that the capacity on file matches the steel in the ground. And contractors can use it during bids, because a 1,000 gallon tank is a very different removal job than a 275.

The calculator supports four shapes: horizontal cylinders, vertical cylinders, rectangular tanks, and the oval profile common on residential heating oil tanks. It accepts dimensions in inches, feet, centimeters, or meters, and it includes presets for the most common residential and commercial tanks so you can skip measuring entirely when your tank matches a standard size.

How the math works

Every result starts from the same conversion: one US gallon equals 231 cubic inches. The calculator converts your dimensions to inches, computes the tank's volume in cubic inches, then divides by 231.

For a full horizontal or vertical cylinder, the volume is the circular cross section times the length: pi times the radius squared times the tank's length (or height, for a vertical tank). A rectangular tank is simply length times width times height. An oval tank is treated as an ellipse: pi times half the width times half the height, times the length.

Partial fills are where the real math lives. When you enter a dipstick reading for a horizontal cylinder, the calculator uses the exact circular segment formula rather than an approximation. The liquid's cross section equals the radius squared times the inverse cosine of (radius minus liquid height) over radius, minus (radius minus liquid height) times the square root of (2 times radius times height minus height squared). Multiply that cross section by the tank length and you have the exact partial volume. This matters because fill height and volume are not proportional in a horizontal cylinder. The first few inches at the bottom hold very little, the middle inches hold the most, and the curve flattens again near the top.

Vertical cylinders and rectangular tanks are easier: volume scales linearly with liquid height, so half the height really is half the volume. For oval tanks, the calculator scales the circular segment math to the elliptical cross section. That approach is a close approximation, not a perfect integral, which is one reason the tool also offers a printable strapping chart generator for compliance work where the numbers get scrutinized.

The weight figure shown with each result multiplies gallons by the density of the fuel you select, using values from ASTM specifications stored in the tool's data file. Diesel #2 and heating oil #2 are 7.10 pounds per gallon, for example. For weight math across every fuel and any volume, the fuel weight calculator goes deeper.

When to use this

Before a fuel delivery. You have a 275 gallon heating oil tank reading 12 inches on the stick. The calculator tells you what those 12 inches mean in gallons, so you can order the right amount instead of guessing and having the driver stop short.

Selling or buying a house with a tank. A buyer's inspector reports an oil tank of unknown size. Measuring the tank's length and diameter takes two minutes, and the calculator turns those measurements into a capacity figure that belongs in the disclosure paperwork. Capacity also drives removal pricing, so once you know the gallons you can estimate removal costs by state before negotiating.

Facility compliance records. Federal UST regulations under the EPA UST program require owners to know what they have in the ground. If a tank's registered capacity looks wrong, computing volume from measured dimensions is the fastest sanity check before you involve anyone else.

Contractor bidding. A removal or installation bid depends on tank size, and the customer often does not know it. A contractor on site with a tape measure can confirm capacity in the driveway. If the project includes a new tank, the directory lists tank installation contractors in Texas and every other state.

Gas station underground tank sizes

Gas station tanks are far larger than most people expect. A typical station stores its fuel in horizontal cylindrical USTs of 6,000 to 20,000 gallons each, buried under or beside the forecourt.

The common sizes follow standard dimensions. A 6,000 gallon UST is about 8 feet in diameter and 16 feet long. An 8,000 gallon tank keeps the 8 foot diameter and stretches to about 21 feet. The 10,000 gallon size, one of the most common at modern stations, runs about 8 feet by 27 feet. A 12,000 gallon tank is roughly 8 feet by 32 feet. Above that, diameters step up to 10 feet: a 15,000 gallon tank is about 25 and a half feet long, and a 20,000 gallon truck stop tank is about 34 feet long. All of these are available as one-click presets in the calculator.

How many tanks a station has depends on volume and product mix. A small rural station selling around 1,500 gallons a day might run two 6,000 gallon tanks, one regular and one diesel. A mid-sized station moving 4,000 gallons a day typically runs three 10,000 gallon tanks covering regular, premium, and diesel. A high volume station selling 8,000 gallons a day steps up to four 12,000 gallon tanks, and a truck stop pushing 15,000 gallons a day commonly installs four 20,000 gallon tanks.

The calculator includes a throughput sizing tool built on those same tiers: enter daily gallons sold and it suggests a tank size and count. A companion days-of-supply tool divides tank size by daily throughput, with a reorder recommendation at 25 to 30 percent remaining to cover typical 2 to 3 day delivery scheduling.

What this estimate doesn't account for

The calculator computes ideal geometric volume. Real tanks deviate from the ideal in a few specific ways.

Wall thickness is ignored. Dimensions are treated as internal, so if you measured the outside of the tank, actual capacity is slightly less than the result. On a small residential tank the difference is modest; on a large UST it can be tens of gallons.

End caps are assumed flat. Many commercial cylindrical tanks have dished or rounded heads that add volume beyond the straight shell. The preset dimensions are calibrated to nominal capacities, but custom dimension entries for tanks with formed heads will read slightly low.

Internal hardware is invisible to the math. Fill tubes, suction lines, baffles, and interstitial monitoring equipment all displace liquid.

Temperature is not corrected. Petroleum products expand and contract with temperature, so a tank gauged on a 95 degree afternoon holds fewer pounds of fuel per gallon than the same reading in January. The math here is volume only.

Finally, a tilted tank throws off dipstick math. The partial fill formula assumes the tank is level; a tank pitched toward one end reads differently depending on where you drop the stick. For anything feeding a compliance record, federal release detection rules in 40 CFR 280 expect measurement practices that hold up to scrutiny, so verify against manufacturer documentation.