Tank volume · Dip

Tank volume calculator with gallons per inch

Know the real space left before the tanker starts pumping.

Enter tank diameter, length or height, and the liquid level, and get the volume, ullage and gallons per inch.

Last updated 2026-09-27. Math runs in your browser, no data leaves your computer.

Measure inside dimensions if you can, since the wall thickness of a large steel tank takes a real amount of volume off the outside figure. The level is the dip or gauge reading from the inside bottom of the shell.

Orientation changes the answer a great deal, because only a vertical tank gains the same volume for every inch of level.

Keep every length in the unit you pick here, since a mix of feet and inches is the easiest way to get a volume that is 12 times off.

Take it from the tank nameplate or drawing, because a tape round the outside includes insulation and wall.

Use the straight part of the shell only, since the tool treats the heads as flat and does not count a dished end.

Measure from the inside bottom, and on a horizontal tank dip at the middle of the shell where the diameter is true.

Before the booking, screen the name on the invoice. Shipment pre-check is on the paid plans, from USD 59 a month.

General guidance only. Verify against the cited primary sources before you commit to a shipment, declaration, or contract.

How the partial fill is worked out

Overfills at delivery usually start with a dip reading turned into a percentage in someone's head. On a horizontal tank the level and the volume do not move together, so the space at the top is smaller than a straight percentage suggests, and the last few hundred gallons of a delivery end up in the bund.

A vertical tank is a straight cylinder, so the liquid volume is pi times the radius squared times the level. A horizontal tank uses the circular segment area under the liquid, r squared times arccos((r minus h) / r) minus (r minus h) times the square root of (2rh minus h squared), multiplied by the shell length. Gallons per inch at the current level is the surface width times the length, taken over one inch.

Cubic inches convert at 231 per US gallon and cubic centimeters at 1,000 per liter, both per NIST Special Publication 811, where a US gallon is 3.785412 liters. The ends are treated as flat, so a tank with dished heads holds more than the tool shows.

Worked example: topping up a horizontal tank

The booking. A horizontal storage tank is 96 inches in diameter and 240 inches long, holding 7,520 US gallons when full. The operator dips 72 inches, reads that as 75% full, works out 25% of space or 1,880 gallons, and books a delivery of that size, which looks fine on paper.

The failure. At 72 inches a horizontal cylinder is 80.4% full, holding 6,050 gallons, so the real space is only 1,470 gallons. The driver pumps 410 gallons more than the tank can take, and the site either stops the transfer with product left in the tanker and pays for the return, or cleans the overflow out of the bund.

The fix. Put the dip into the tool with the horizontal setting and it returns 6,050 gallons in the tank and 1,470 gallons of ullage. The operator books 1,400 gallons, which fits inside the space with room to spare, and the tanker leaves empty with the tank short of the top.

Loading an ISO tank rather than a fixed tank, where the fill has to sit inside regulatory limits? The liquid expansion and ullage calculator sizes the vapor space for the temperature rise in transit.

Reading a flow meter or pump curve in a different unit from your tank chart? The plant unit converter switches pressure, flow and temperature between the common plant units.

Frequently asked

How do I calculate the volume of a horizontal cylinder tank at a given liquid height?

Work out the area of the circular segment below the liquid, then multiply by the tank length. The segment area is r squared times arccos((r minus h) / r), minus (r minus h) times the square root of (2rh minus h squared), where r is the radius and h the liquid height. For a 96 inch diameter, 240 inch long tank with 72 inches of liquid, that gives 6,050 US gallons out of 7,520 full.

What is gallons per inch and why does it change?

Gallons per inch is how much the volume changes for each inch of level, which is what you need to turn a dip reading into a delivery size. In a vertical tank it is constant, at pi times r squared divided by 231 cubic inches per gallon. In a horizontal tank it is largest at the middle and falls toward the top and bottom, so a 96 by 240 inch tank moves 86.4 gallons per inch at a 72 inch level.

Does the calculator include dished or elliptical heads?

No, it treats the ends as flat. Dished, elliptical and hemispherical heads add volume beyond the straight shell, so for custody transfer or billing use the tank manufacturer strapping chart, which is calibrated for the real heads and any internal fittings.

Why is a horizontal tank not half full at a quarter of the depth?

Because the tank is narrow at the bottom and widest at the middle. At 25% of the diameter a horizontal cylinder holds about 19.6% of its volume, and at 75% of the diameter it holds about 80.4%, so reading level as a straight percentage overstates the space at the top.

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Sourzi shows what official files say. It is not customs or legal advice. For a binding answer, ask a licensed customs broker, a CBP ruling or an Australian Border Force Tariff Advice.

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