Phage Half-Life Calculator

∞ generated and posted on 2017.04.17 ∞
∞ updated on 2022.06.05 ∞

The time it takes for half of a phage population to adsorb is easy to calculate as approximately the reciprocal of the product of bacterial concentration and the phage adsorption rate constant.

Please cite as:

Stephen T. Abedon
Phage Half-Life Calculator.

Click here for calculator or see immediately below for further explanation and discussion.

For discussion, see Abedon, S. T. (2011). Envisaging Bacteria as Phage Targets. Bacteriophage 1(4):228-230. See also: .


Note that phage half-life is equal to

-ln(0.5)/([adsorption rate constant]×[constant bacterial density]),

as rounds up to phage mean free time, which is equal to

1/([adsorption rate constant]×[constant bacterial density]).

Keep in mind that you cannot substitute CFUs (colony-forming units) per unit volume for bacterial density (i.e., concentration) unless the phage adsorption rate constant as measured is based on CFUs rather than strictly on numbers of individual bacteria. The problem is that a CFU can consist of more than one bacterium (e.g., Streptococcus) and phages should adsorb to multiple bacteria faster than they adsorb to a single bacterium .


For discussion of phage adsorption theory, see

For a multiplicity of infection calculator, see

See also Bacterial Half-Life Calculator.

Don't forget to be consistent with your units. Mixing minutes with hours, milliliters with liters, or absolute numbers with concentrations simply will not do! (Regardless, I'm assuming that volumes are in millimeters and time is in minutes.) And if you need a refresher on scientific notation, there is always Wikipedia

= m
above is set to 1 if left blank or not number or ≤ 0
= n
above is set to 0 if left blank or not number or < 0

= m
above is set to 2.5 if left blank or not number or ≤ 0
= n
above is set to -9 if left blank or not number or > 0

k value is defaulted at 2.5 × 10-9 ml-1 min-1 from Stent (1963)
may be greater or lower but must be defined to calculate MOIactual
the larger the number, the faster the phage adsorption