A gallon of regular gasoline weighs about 6.0-6.3 pounds at 60°F, while a gallon of diesel weighs more — roughly 6.7-7.1 pounds, since diesel is denser than gasoline. That few-pound difference per gallon adds up fast: a full 15-gallon gas tank adds roughly 90-95 pounds to a car’s weight, and a full 100-gallon diesel tank on a work truck adds close to 700 pounds. This guide breaks down exact weights by fuel type and grade, why the number isn’t perfectly fixed, and where it actually matters for payload, towing, and fuel economy math.
Key Takeaways
- Regular gasoline weighs about 6.0-6.3 lbs per gallon at 60°F; diesel weighs more, at roughly 6.7-7.1 lbs per gallon.
- Diesel is about 14% heavier than gasoline per gallon due to its higher density (J.D. Power, retrieved 2026-08-17).
- Fuel grade matters too — midgrade gas runs closer to 6.35 lbs/gallon and premium closer to 6.27 lbs/gallon, both slightly heavier than regular’s roughly 6.07 lbs/gallon.
- A full 15-gallon gas tank adds roughly 90-95 lbs to a vehicle’s total weight — a real factor in GVWR and payload calculations, not just a rounding error.
- Fuel weight changes slightly with temperature: gasoline expands and gets very slightly lighter per gallon as it warms up, and contracts (gets denser) as it cools.
How Much Does a Gallon of Gas Actually Weigh?
At the standard reference temperature of 60°F, a gallon of gasoline weighs approximately 6.2 pounds. That figure shifts slightly by grade: regular fuel comes in around 6.073 lbs per gallon, midgrade runs closer to 6.35 lbs, and premium sits around 6.27 lbs, based on differences in additive packages and blend composition between grades (Vevor, retrieved 2026-08-17).
These are all approximations rather than fixed constants, because gasoline is a blended product whose exact density varies slightly by refinery batch, region, and seasonal formulation. For everyday purposes — estimating how much weight a full tank adds to your car — 6.0 to 6.3 lbs per gallon is accurate enough for any practical calculation.
How Much Does a Gallon of Diesel Weigh?
Diesel fuel is officially defined at 6.943 lbs per gallon at 59°F, though real-world diesel commonly weighs closer to 7.1 lbs per gallon depending on exact density and grade, with the full range running from about 6.70 to 7.25 lbs/gallon (TCS Fuel, retrieved 2026-08-17). That makes diesel roughly 14% heavier than gasoline per gallon — a meaningful difference once you’re filling a large tank rather than a small one.
This matters most for commercial trucking and fleet operators, where a large diesel tank’s fuel weight is a real line item in total vehicle weight calculations, not a rounding error. A semi truck with twin 100-gallon-plus tanks can carry 1,400+ lbs of diesel alone when both tanks are full.
Why a Full Tank Actually Affects Your Vehicle’s Weight
Fuel counts toward your vehicle’s total weight the same as passengers and cargo do, and that total is what your Gross Vehicle Weight Rating (GVWR) caps. Curb weight — the number printed on your door jamb sticker — doesn’t include fuel, passengers, or cargo, so filling up directly eats into your available payload capacity (Lytx, retrieved 2026-08-17).
For a typical 15-gallon car tank, that’s about 90-95 lbs of gasoline — noticeable but rarely a real constraint for a passenger car’s payload. It matters far more on trucks and trailers running close to their rated limits, where our guide to GVWR and heavy-duty truck ramps and hitch cargo carrier tongue-weight guide both cover how every pound — fuel included — factors into a weight rating that’s easier to hit than most owners expect. If you’re loading a truck bed or roof rack near its rated capacity, a full tank of fuel is one more line item worth accounting for, not an afterthought.
Does Fuel Weight Actually Affect Gas Mileage?
Yes, marginally. A heavier vehicle takes more energy to accelerate, so a full tank versus a nearly empty one does cost a small amount of fuel economy — generally cited as a roughly 1% mpg penalty for every 100 lbs of added weight across most passenger vehicles. For a 90-lb full tank, that’s a small enough effect that it rarely changes real-world driving decisions, but it’s part of the same physics that makes overall vehicle weight matter for efficiency; our Smart car weight guide covers how a car’s baseline curb weight (fuel aside) drives much bigger swings in fuel and energy efficiency than the fuel itself does.
Does Fuel’s Weight Change With Temperature?
Yes, slightly. Like most liquids, gasoline expands as it warms and contracts as it cools, meaning a gallon measured at a hot pump on a summer day contains marginally less mass (and slightly less energy) than a gallon measured on a cold winter morning, even though both fill the same gallon-marked container. This effect is small enough that it doesn’t meaningfully change day-to-day weight calculations, but it’s the reason fuel weight specs are always quoted at a reference temperature (typically 59-60°F) rather than as a single flat number.
Frequently Asked Questions
How much does a full 20-gallon gas tank weigh?
Roughly 120-126 lbs of gasoline, using the 6.0-6.3 lbs per gallon range for regular fuel. The exact figure depends on grade and temperature, but this range is accurate for practical estimating.
Is diesel always heavier than gasoline?
Yes, diesel is consistently denser and heavier per gallon than gasoline — roughly 14% more on average — due to differences in the hydrocarbon composition of the two fuels.
Does premium gas weigh more than regular gas?
Slightly, yes, though the difference is small enough (roughly 0.2 lbs per gallon) that it has no meaningful practical impact on vehicle weight or payload calculations.
How much does jet fuel weigh compared to gasoline?
Jet fuel (Jet A) weighs approximately 6.7-6.8 lbs per gallon, close to diesel’s weight and noticeably heavier than gasoline — a critical figure in aviation, where fuel weight directly factors into aircraft weight-and-balance calculations before every flight.
The Bottom Line
A gallon of gasoline weighs roughly 6.0-6.3 lbs, and a gallon of diesel weighs roughly 6.7-7.1 lbs — a difference that’s small per gallon but adds up to real pounds once you’re talking about a full tank. For most drivers, that’s a curiosity more than a practical concern, but for anyone loading a truck, trailer, or RV close to its rated GVWR, fuel weight is a real part of the total that’s easy to overlook until you’re already over the limit. Knowing the actual per-gallon number — not just “fuel is heavy” — is what lets you do that math correctly before you’re at the scale.
