Laundry detergent buying guide - Good Housekeeping Institute- washing powder laundry washing powder washing powders that came ,Powders designed for coloured laundry do not contain a bleaching agent. Packet sizes vary from about 1.76kg to 2.4kg and you should get anywhere from 22 - 30 washes for that.Laundry detergent buying guide - Good Housekeeping InstitutePowders designed for coloured laundry do not contain a bleaching agent. Packet sizes vary from about 1.76kg to 2.4kg and you should get anywhere from 22 - 30 washes for that.