Colony Forming Units Per mL Calculator
Calculate colony forming units per ml with our free science calculator. Uses standard scientific formulas with unit conversions and explanations.
Calculator
Adjust values & calculateExpected Colonies at Each Dilution Step
Formula
The CFU per mL is calculated by multiplying the colony count by the total dilution factor (dilution ratio raised to the power of the number of serial dilution steps), then dividing by the volume of diluted sample that was plated. The total dilution factor converts the count back to the original sample concentration.
Last reviewed: December 2025
Worked Examples
Example 1: Standard Serial Dilution CFU Count
Example 2: Two-Fold Dilution for MIC Testing
Background & Theory
The Colony Forming Units Per mL Calculator applies the following established principles and formulas. Biology is the scientific study of life, encompassing the structure, function, growth, evolution, and distribution of living organisms. At the cellular level, all life is composed of cells, the basic structural and functional units of organisms. Prokaryotic cells lack a membrane-bound nucleus, while eukaryotic cells possess a nucleus and membrane-bound organelles including mitochondria, which generate ATP through oxidative phosphorylation, and ribosomes, which synthesize proteins. Genetics quantifies the inheritance of traits. Gregor Mendel's laws describe how alleles segregate during gamete formation and assort independently for genes on different chromosomes. Punnett squares provide a visual method for calculating the probability of offspring genotypes and phenotypes from known parental genotypes. For a monohybrid cross of two heterozygotes (Aa ร Aa), the expected phenotypic ratio is 3 dominant to 1 recessive. The Hardy-Weinberg equilibrium principle states that allele and genotype frequencies in a population remain constant from generation to generation in the absence of evolutionary forces. If p and q are the frequencies of two alleles at a locus, then p + q = 1 and genotype frequencies are pยฒ, 2pq, and qยฒ for the three possible genotypes. Deviations from equilibrium signal the action of natural selection, genetic drift, mutation, migration, or non-random mating. Population growth follows two primary models. Exponential growth, N = Nโeสณแต, describes unlimited growth where Nโ is the initial population, r is the intrinsic rate of increase, and t is time. Logistic growth incorporates carrying capacity K, describing how growth slows as population approaches the environment's maximum sustainable size: dN/dt = rN(1 โ N/K). Enzyme kinetics describes the rate of enzyme-catalyzed reactions. The Michaelis-Menten equation, v = Vmax[S]/(Km + [S]), relates reaction velocity v to substrate concentration [S], maximum velocity Vmax, and the Michaelis constant Km, which equals the substrate concentration at half-maximal velocity. DNA replication relies on complementary base pairing: adenine pairs with thymine (two hydrogen bonds) and guanine with cytosine (three hydrogen bonds), ensuring faithful copying of genetic information.
History
The history behind the Colony Forming Units Per mL Calculator traces back through the following developments. The systematic study of living things began with Aristotle (384โ322 BCE), who classified over 500 animal species and wrote foundational texts on anatomy, reproduction, and animal behavior. His scala naturae ranked organisms in a hierarchy from simple to complex and influenced biological thought for two millennia. Theophrastus, his student, applied similar methods to plants. Carl Linnaeus established modern taxonomy in Systema Naturae (1735), introducing the binomial nomenclature system that assigns each organism a genus and species name. His hierarchical classification system โ species, genus, family, order, class, phylum, kingdom โ provided the organizational framework that biologists still use, now extended to seven ranks and supplemented by cladistics. Charles Darwin and Alfred Russel Wallace independently developed the theory of evolution by natural selection, which Darwin published in On the Origin of Species in 1859. Darwin argued that heritable variation exists within populations, that organisms with advantageous traits survive and reproduce at higher rates, and that this differential reproduction gradually changes the character of populations over generations. This unified all of biology under a single explanatory framework. Gregor Mendel's meticulous pea plant experiments, conducted from 1856 to 1863 and published in 1866, established the particulate nature of inheritance and the laws of segregation and independent assortment. Overlooked until 1900, when three botanists independently rediscovered his work, Mendel's laws laid the foundation for the science of genetics. James Watson and Francis Crick, building on Rosalind Franklin's X-ray crystallography data, determined the double-helix structure of DNA in 1953, revealing the physical basis of heredity and the mechanism by which genetic information is stored and copied. The Human Genome Project, a 13-year international collaboration, published the complete sequence of the human genome in 2003, comprising approximately 3.2 billion base pairs. The development of CRISPR-Cas9 gene editing by Jennifer Doudna, Emmanuelle Charpentier, and colleagues from 2012 onward opened an era of precise genome modification with transformative implications for medicine, agriculture, and basic research.
Frequently Asked Questions
Formula
CFU/mL = (Colony Count x Dilution Ratio^Steps) / Volume Plated (mL)
The CFU per mL is calculated by multiplying the colony count by the total dilution factor (dilution ratio raised to the power of the number of serial dilution steps), then dividing by the volume of diluted sample that was plated. The total dilution factor converts the count back to the original sample concentration.
Frequently Asked Questions
How do you calculate CFU per mL from serial dilutions?
To calculate CFU/mL from serial dilutions, use the formula: CFU/mL = (Number of colonies x Total dilution factor) / Volume plated (mL). The total dilution factor is the product of all individual dilution steps. For ten-fold serial dilutions, the total dilution at step N is 10^N. For example, after 5 serial 1:10 dilutions, the total dilution factor is 10^5 = 100,000. If you counted 180 colonies from 0.1 mL plated at this dilution: CFU/mL = (180 x 100,000) / 0.1 = 1.8 x 10^8. Always ensure your colony counts fall within the countable range of 25-250 colonies per plate for accurate results.
What is dilution plating and how do I calculate colony counts?
Dilution plating estimates bacterial concentration by serially diluting samples and plating on agar. Count colonies on plates with 30-300 colonies. Calculate: CFU/mL = colonies / (dilution factor * volume plated). For example, 150 colonies on a 10^-5 dilution with 0.1 mL plated = 1.5 x 10^8 CFU/mL.
Is my data stored or sent to a server?
No. All calculations run entirely in your browser using JavaScript. No data you enter is ever transmitted to any server or stored anywhere. Your inputs remain completely private.
Can I use the results for professional or academic purposes?
You may use the results for reference and educational purposes. For professional reports, academic papers, or critical decisions, we recommend verifying outputs against peer-reviewed sources or consulting a qualified expert in the relevant field.
What inputs do I need to use Colony Forming Units Per mL Calculator accurately?
Each field is labelled with the required unit (metric or imperial). Gather your source values before starting โ for example, a weight measurement in kilograms, a distance in metres, or a dollar amount โ and enter them exactly as measured. The formula section on this page lists every variable and explains what each represents.
Does Colony Forming Units Per mL Calculator work offline?
Once the page is loaded, the calculation logic runs entirely in your browser. If you have already opened the page, most calculators will continue to work even if your internet connection is lost, since no server requests are needed for computation.
References
Reviewed by Daniel Agrici, Founder & Lead Developer ยท Editorial policy