If you don't know the gallon capacity of your aquarium, it can be determined by dividing the cubic inches by 371. If you want to know the size in liters, divide the cubic centimeters by 1000.

Filter(s) need to have an hourly rate of at least 4 to 5 times the tank's capacity.

Purchase gravel (substrate) at a rate of one pound per gallon per inch of depth. Thus a 10 gallon aquarium with a depth of two inches would require 20 pounds and a 30 gallon tank with one inch of gravel would require 30 pounds.

The heater wattage should be a minimum of 5 times that of the tank size in gallons (15 watts per liter). This can be split among multiple heaters.

Metric Conversions.

Volume
1 gallon = 3.78541 liters
1 liter = 0.264172 gallons
Length
1 inch = 2.54 centimeters
1 centimeter = 0.393701 inches
Temperature
Fahrenheit = (Celsius * 1.8) +32
Celsius = (Fahrenheit - 32) / 1.8