Colonies of bacteria are collection of bacteria of the same kind that cluster all together and form colonies. To knowing the growing of the bacteria that can calculate of number of bacterial colonies. Remember the number of colonies can achieve more than 300 colonies, so that necessary of the tools it called Colony Counter to easier calculation the number of bacterial colonies the colony counter generally it is still manual, just rely on memory of lab attendant. The processing still manual like this will impact of slow process calculation and low of quality the result was obtained. The condition of process of calculation like that need to perfect because the burden of the laborite is rising. The method of trial to do is prepare the bacteria that already in incubator so it forms a colony of petri dish. Bacterial colony calculations in a petri dish with the factor dilution 10-1 -10-5 five times over to 5 different observer used tools colony counter. Then, the result calculation 5 observer be compared with the result of calculate that can do as manual and be sought value of average with percentage value of deviation. So that, percentage value of deviation that can be obtained from the result of compared calculate of colonial bacteria in observer 1 is 0.016%, observer 2 is 0.027%, observer 3 is 0.014%, observer 4 is 0.011% and observer 5 is 0.035%. So that percentage of value that obtained. Thus, this tools it says here it is due to error below 10%.