To give a more accurate answer we would need to know the gallons of gas your car holds.
Cars can have different size gas tanks but a cars gas tank is between 12 gallons to 16 gallons.
Assuming your car has a 12 gallon gas tank and your car gets the 25 mpg range on gasoline then the 12 gallon tank of gas should last you 300 miles.
But of course you should top off the gas tank before it does get to empty because running the gas tank empty can get you stranded as well as ruin your fuel pump.
If your gas tank is 16 gallons then a tank of gas should last you 400 miles.
Your owners manual should say what size gas tank you have but if not just wait till the gas tank reads almost empty and then fill the tank up and see how many gallons you can put in the tank.
Assuming you can fill the gas tank with 16 gallons then that 16 gallons should last you up to 400 miles.