What is the Cost to Fill Gas Tank Calculator?
This calculator tells you how much it will cost to fill your vehicle's fuel tank. By combining your tank's capacity with the current price per gallon, it gives a quick dollar estimate for a full fill-up. You can also enter how full your tank already is, so the tool only counts the fuel you actually need to add.
How to use it
Enter three values: your tank size in gallons (most cars hold 12–18 gallons), the price per gallon at the pump, and your current tank level as a percentage (use 0% for an empty tank). Press calculate to see the cost to fill, the gallons you'll buy, and the cost of a complete fill from empty.
The formula explained
The core formula is simple: cost = tank size × price per gallon. When you account for fuel already in the tank, the calculator first finds the gallons needed as tank size × (1 − level / 100), then multiplies by the price per gallon. A tank that is 25% full only needs 75% of its capacity refilled.
$$\text{Cost} = \text{Tank Size} \times \left(1 - \frac{\text{Level \%}}{100}\right) \times \text{Price/Gal}$$
Worked example
Suppose you have a 15-gallon tank, gas costs $3.50 per gallon, and the tank is empty (0%). Gallons needed = \(15 \times (1 - 0) = 15\) gallons. Cost = \(15 \times \$3.50 =\) $52.50. If the tank were already 50% full, you'd need 7.5 gallons, costing $26.25.
$$\text{Cost} = 15 \times \left(1 - \frac{0}{100}\right) \times \$3.50 = \$52.50$$
FAQ
Where do I find my tank size? Check your owner's manual or the manufacturer's website — it's listed as fuel tank capacity.
What if I don't know my current level? Leave it at 0% to estimate the cost of a complete fill from empty, which is the maximum you'd ever pay.
Does this work for diesel or any currency? Yes. The math is the same for any fuel type and any currency — just enter the price per unit you pay.
