Tanker weight calculator: gallons to pounds and the legal load

How the tanker weight calculator works

• Product weight = gallons × pounds per gallon.
• Gross weight = product weight + rig empty weight; compared with your gross limit.
• Max gallons by weight = (gross limit − empty weight) ÷ pounds per gallon, rounded down.
• Max gallons by outage = shell × (1 − outage) ÷ (1 + expansion × degrees to the reference temperature).
• Legal load = the smaller of the two.

Weights per gallon the calculator uses

Weight per gallon is specific gravity times 8.34 lb, the weight of a gallon of water. Real products vary with blend and temperature, so for anything else, choose "Other" and enter the figure from the shipping paper or safety data sheet.

Outage and the reference temperature

Federal rules require at least 1% outage, empty space, in each cargo tank or compartment for liquids, 5% for materials poisonous by inhalation, measured at 115 °F for an uninsulated tank or 105 °F for an insulated one. Source A cold load expands toward that reference temperature, so the space you leave at the rack has to cover the growth. The optional expansion input does that math when you have the product's coefficient.

Worked example

A rig weighing 32,000 lb empty, with a 9,300 gallon tank, is offered 7,000 gallons of diesel. At 7.01 lb a gallon, the load weighs 49,070 lb and the truck grosses 81,070 lb: 1,070 lb over an 80,000 lb limit. The calculator shows the legal load at 6,847 gallons, limited by weight. The same tank with gasoline at 6.2 lb a gallon could legally take about 7,740 gallons.

What the result means

The gross limit on the Interstate is 80,000 lb unless the bridge formula sets less. Source Axle groups have their own limits under the same formula Source, so check them with the bridge formula calculator. If the result shows "limited by outage," the product is light enough that the tank fills before the truck gets heavy, which is rare for liquids hauled in semi tankers.

Getting the empty weight right

The result is only as good as the empty weight you enter. Weigh the tractor and empty trailer together on a certified scale with the fuel tanks at the level you usually leave the terminal with, the driver aboard, and any pump, hoses and gear you carry. A rig weighed with near-empty fuel tanks can be close to a thousand pounds lighter than it runs, which is enough to turn a legal load into a ticket.

Compartments and axle balance

On a compartmented tank, where each product sits changes the axle weights even when the gross stays the same. Heavy product in the front compartment loads the drive axles; heavy product at the rear loads the trailer tandem. When a delivery splits several products, plan the compartments so the heaviest one sits over the middle of the trailer, and remember that unloading part of the load at the first stop shifts the balance for the rest of the trip.

Common mistakes

• Using a generic weight per gallon instead of the shipper's figure.
• Filling a cold product to the outage line with no room for it to grow.
• Checking gross weight but not axle groups.
• Forgetting the weight of hoses, pumps and a full set of fuel tanks.

License note

Any truck carrying tanks over 119 gallons each and 1,000 gallons or more in total is a tank vehicle, which needs the N endorsement, or X with placarded hazmat. Source More on capacities in how many gallons a tanker truck holds and the tanker truck guide. Our desk books non-hazmat tanker loads; see tanker dispatch or the GearLoads home page.