Car CO2 Emissions Calculator
Every gallon of fuel a car burns releases a predictable amount of carbon dioxide, and this car CO2 emissions calculator turns the fuel you use into an estimate of your tailpipe carbon. Enter the gallons of fuel consumed, for a single trip or a whole month, along with the CO2 emission factor for your fuel, and the tool multiplies the two to show the pounds of carbon dioxide produced. Gasoline carries an emission factor of roughly 19.6 pounds of CO2 per gallon, while diesel is higher because it packs more carbon into each gallon. The result is a clear, deterministic figure you can use to compare vehicles, understand the impact of a long drive, or see how much carbon a more efficient car would save. It surprises many people that a gallon of liquid fuel can produce nearly twenty pounds of gas, but most of that weight is oxygen drawn from the air during combustion. Because fuels and blends differ, the emission factor is left as an editable input rather than fixed, so you can match it to what your vehicle actually burns. The calculation is a single multiplication, shown in the formula below, with a worked example that reconciles exactly to the calculator defaults.
Tailpipe carbon is fuel times its emission factor: CO2 = gallons x factor per gallon. Burning 12 gallons of gasoline at 19.6 lb CO2 per gallon releases about 235.20 lb of carbon dioxide.
Car CO2 emissions formula
CO2 (lb) = G x F
G = gallons of fuel burned
F = emission factor in pounds of CO2 per gallon
Gasoline F is about 19.6, diesel about 22.4
Each gallon of fuel releases a fixed amount of carbon dioxide, so multiplying the gallons burned by the emission factor gives the total CO2 produced.
Worked example
You burn 12 gallons of gasoline, using an emission factor of 19.6 pounds of CO2 per gallon.
- CO2 = gallons x factor
- CO2 = 12 x 19.6
- CO2 = 235.2 pounds
The fuel releases about 235.2 pounds of CO2. These are the calculator's default inputs, so the result above matches the widget exactly.
Car CO2 emissions calculator: frequently asked questions
How is car CO2 calculated from fuel?
Burning a gallon of fuel releases a fixed amount of carbon dioxide, so emissions equal the gallons used multiplied by the emission factor per gallon. Gasoline produces roughly 19.6 pounds of CO2 per gallon. Burning 12 gallons therefore releases about 235.2 pounds. The calculator multiplies your fuel volume by the factor you choose to estimate tailpipe CO2.
What emission factor should I use?
A common reference value for gasoline is about 19.6 pounds of CO2 per gallon, while diesel is higher at roughly 22.4 pounds per gallon because it is denser and contains more carbon. The exact figure depends on the fuel and its blend, so the factor is left as an editable input. Pick the value that matches the fuel your vehicle uses.
Why does burning one gallon make so much CO2?
It seems surprising that a gallon of liquid weighing about six pounds can produce nearly twenty pounds of carbon dioxide, but most of that weight comes from oxygen pulled out of the air during combustion. Each carbon atom in the fuel combines with two oxygen atoms to form CO2, so the gas produced weighs far more than the fuel that started it.
How can I lower my driving emissions?
Because emissions scale directly with fuel burned, anything that cuts fuel use cuts CO2: driving fewer miles, improving fuel economy, keeping tyres inflated and easing off hard acceleration. Switching to a more efficient or electric vehicle has the largest effect. The calculator makes the link clear, since halving the gallons halves the carbon dioxide.
What is the car CO2 emissions formula?
CO2 emitted equals gallons of fuel burned multiplied by the emission factor per gallon. With 12 gallons of gasoline and a factor of 19.6 pounds per gallon, that is 12 x 19.6, which equals 235.2 pounds of CO2.
Official sources
- Environmental health and emissions guidance: US Centers for Disease Control and Prevention (CDC). As at 25 June 2026.
Reviewed by the CalculatorHub team, edited by James Graham, 25 June 2026. See our methodology. This is general information, not financial, tax, legal or investment advice.