It's not the volts, it's the watts
In the US, our typical household electricity is 120 volts, but it's the heater wattage
that is the number of interest. The target wattage of the heater(s) depends on how cold the room is and how warm you need to make the tank water. First, take the average room temp and subtract that number from the desired tank temperature to get the total degree of temp increase desired.
Basic rule of thumb for a 55"ish" gallon tank:
To raise the water temp above room temp by
* + 5F = 150 to 175 watts.
* + 10F = 200 to 225 watts.
* + 15F = 400 to 500 watts. (Requires 2 x 200W heaters )
Your wattage needs may vary a bit depending on how much water is in the tank, tank cover (or not), and room air flow around the tank.
NOTE: on any tank 4' and over, I recommend using two smaller heaters rather than a single large one to reach the total wattage. That way, you can buy two slightly higher total
wattage-than-needed heaters, giving a reserve capacity, and even if one heater fails, you aren't likely to fry or freeze your fish before you notice a problem. Two heaters also gives much more even tank temps if you place them correctly.
In my 55 gallon, I have two 100 watt heaters and elevate my tank to about +5 degrees above the room temp.