The amount of laundry detergent to water for carpet cleaning depends on the type of detergent being used. Generally, it is recommended to use 1/4 cup of liquid laundry detergent per gallon of warm water when using a steam cleaner or extractor. For spot cleaning with a sponge and bucket, mix 2 tablespoons of liquid laundry detergent in one quart (32 ounces) of warm water. Always test any solution on an inconspicuous area before applying it to the entire carpet.