How Fuel Shortfall Calculator Works?
This tool works by subtracting the fuel in your tank from the fuel the trip requires. The result is the extra gallons you need to buy.
Find fuel required
Divide trip miles by miles per gallon (MPG). The Fuel Consumption Calculator gives this figure.
Enter fuel required
Type the gallons the trip needs, for example 18.5 gallons (70 L).
Enter fuel in the tank
Type the gallons currently in the tank, for example 7 gallons.
Read the shortfall
The tool returns the gallons to add. A result of 0 means the tank already holds enough.
Fuel Shortfall Calculator Formula
The formula is Shortfall = max(0, Fuel Required − Fuel in Tank).
Shortfall = max(0, Fuel Required − Fuel in Tank)Formula variables
- Fuel Required
- Gallons needed to finish the trip.
- Fuel in Tank
- Gallons already on board.
- max(0, …)
- Stops the result from going below 0.
Worked example
- Fuel Required for Trip: 18.5 gallons
- Fuel Currently in Tank: 7 gallons
- Subtract: 18.5 − 7 = 11.50 gallons (43.5 L) to add.
Result: 11.50 (gallons needed)
At $3.65 per gallon, an 11.5-gallon shortfall costs $41.98. Adding a 10% buffer to the required fuel protects against detours.
Fuel Shortfall Calculator Conversion Table
The table shows gallons to add for 4 trip fuel needs and 3 tank levels.
Rows: Fuel Required for Trip (gallons). Columns: Fuel Currently in Tank (gallons). Cells: gallons needed.
| gallons | 3 gallons | 7 gallons | 12 gallons |
|---|---|---|---|
| 10 gallons | 7.00 | 3.00 | 0.00 |
| 18.5 gallons | 15.50 | 11.50 | 6.50 |
| 25 gallons | 22.00 | 18.00 | 13.00 |
| 30 gallons | 27.00 | 23.00 | 18.00 |
A trip needing 10 gallons with 12 gallons in the tank shows 0, so no fuel stop is needed before leaving.
What is Fuel Shortfall Calculator?
The Fuel Shortfall Calculator is a tool that finds how much more fuel you need before a trip. The tool prevents running short partway through a drive.
Drivers often start a trip with a partly full tank. The shortfall shows the exact gallons to buy, not a full fill-up.
The calculator works for vehicles, boats, and generators with known fuel needs.
What are the uses of Fuel Shortfall Calculator?
There are 4 main uses of the Fuel Shortfall Calculator: preparing for a trip, refueling boats before outings, filling generators before storms, and planning fuel cans for remote travel.
Preparing for a trip
Drivers buy only the gallons the trip needs.
Refueling boats before outings
Boaters add enough fuel for the planned hours on the water.
Filling generators before storms
Homeowners calculate fuel for a set number of run hours.
Planning fuel cans for remote travel
Off-road drivers carry the shortfall in jerry cans.
Need every metric in one place? Open the main MPG Cost Calculator or browse all 101 fuel calculators.