How Fuel Top-Up Calculator Works?
This tool works by finding the empty share of your tank, multiplying by tank capacity, and pricing those gallons. The result is the cost to fill the tank from its current level.
Read the fuel gauge
Estimate the current level as a percentage. A quarter tank equals 25%.
Enter the current percentage
Type the gauge reading into the first field.
Enter tank capacity and price
Type the tank size in gallons and the price per gallon.
Read the top-up cost
The tool returns the cost to fill the remaining space.
Fuel Top-Up Calculator Formula
The formula is Top-Up Cost = ((100 − Current %) ÷ 100) × Tank Capacity × Price per Gallon.
Top-Up Cost = ((100 − Current %) ÷ 100) × Tank Capacity × PriceFormula variables
- (100 − Current %) ÷ 100
- Empty fraction of the tank.
- Tank Capacity
- Full tank size in US gallons.
- Price
- Pump price per US gallon (3.785 L).
Worked example
- Current Tank Fraction %: 25%
- Tank Capacity: 16 gal
- Price per Gallon: $3.60/gal
- Empty fraction: (100 − 25) ÷ 100 = 0.75.
- Gallons to add: 0.75 × 16 = 12 gallons (45.4 L).
- Cost: 12 × $3.60 = $43.20.
Result: $43.20 ($ to target)
Fuel gauges read less precisely near the top and bottom of the range. A gauge at 1/4 often means 20% to 30% remaining, so treat the result as a close estimate.
Fuel Top-Up Calculator Conversion Table
The table shows top-up costs for 5 gauge readings and 4 tank sizes, with fuel at $3.60 per gallon.
Rows: Current Tank Fraction % (%). Columns: Tank Capacity (gal). Cells: $ to target.
| % | 12 gal | 16 gal | 20 gal | 26 gal |
|---|---|---|---|---|
| 0% | $43.20 | $57.60 | $72.00 | $93.60 |
| 10% | $38.88 | $51.84 | $64.80 | $84.24 |
| 25% | $32.40 | $43.20 | $54.00 | $70.20 |
| 50% | $21.60 | $28.80 | $36.00 | $46.80 |
| 75% | $10.80 | $14.40 | $18.00 | $23.40 |
Values held constant: Price per Gallon = $3.60/gal.
Topping up a 26-gallon (98.4 L) tank from empty costs $93.60, while topping up a 12-gallon tank from 75% costs $10.80.
What is Fuel Top-Up Calculator?
The Fuel Top-Up Calculator is a tool that prices the fuel needed to fill a tank from its current gauge level. The tool matches what the pump charges at the next stop.
The calculator converts a gauge reading into gallons. Drivers see the cost before reaching the station.
The tool works for any vehicle with a known tank size, including cars, trucks, boats, and generators.
What are the uses of Fuel Top-Up Calculator?
There are 4 main uses of the Fuel Top-Up Calculator: planning the next fill-up, returning rental cars full, budgeting boat refuels, and comparing top-up timing.
Planning the next fill-up
Drivers know the cost before pulling into a station.
Returning rental cars full
Renters price the top-up against the agency refuel fee.
Budgeting boat refuels
Boat owners price the top-up from the marina gauge.
Comparing top-up timing
Drivers compare topping up at 50% with waiting until 25%.
Need every metric in one place? Open the main MPG Cost Calculator or browse all 101 fuel calculators.