Depends on the bacteria and whether its grows as a grape, strand, or ... Most microbiologists obtain an 'OD or optical density' of a broth containing the bacteria. Serial dilute the broth and plate them on agar. They then select the OD that has a 1,000,000 colonies per mL.
Start a overnight culture (primary), next day start a secondary culture, grow them upto 0.6 OD, serially dilute the secindary culture, plate a specific volume (30-50 uL) in agar plate, count CFU. Based on CFU/mL you can determine how much volume will give you 1*10^6 cells. Its very easy if you have microbiology/cell culture training.