# CFU/mL Calculator (Colony Forming Units)

Colony count → CFU/mL with dilution factor and plate volume, plus 30–300 range TNTC/TFTC interpretation. Educational use only.

> Canonical page: https://elysiatools.com/en/tools/cfu-calculator

- **Category:** Education

- **Keywords:** cfu calculator, cfu per ml, colony forming unit calculation, plate count dilution, serial dilution cfu, tntc tftc plate count, countable range 30 300, bacterial enumeration, microbiology calculator, lab calculator

## Overview

Calculate CFU/mL from a colony count, dilution exponent, and plated volume. The calculator applies CFU/mL = colonies × 10ⁿ ÷ plated volume in mL and interprets counts against the 30–300 countable range. Educational use only.

## Inputs

- **Colonies Counted** (number): Colonies on the plate after incubation.
- **Dilution Exponent (10⁻ⁿ)** (number): n such that the plate was seeded from the 10⁻ⁿ dilution tube.
- **Plated Volume (mL)** (number): Volume of diluent spread on the plate (0.1 mL = 100 µL is typical).
- **Original Sample Volume (mL)** (number): Optional original culture volume, for total CFU in the sample.
- **Decimal Places** (number)

## When to use

- Convert colonies counted on a dilution plate into the estimated CFU/mL of the original culture.
- Check whether a plate count falls within the standard 30–300 countable range.
- Estimate total CFU when the original sample volume is also known.

## How it works

- Enter the number of colonies counted on the incubated plate.
- Enter the dilution exponent n for the 10⁻ⁿ dilution used to seed the plate.
- Enter the plated volume in milliliters, such as 0.1 mL for 100 µL.
- The calculator returns CFU/mL, optional total CFU from the original sample volume, and count-quality guidance.

## Use cases

- Microbiology students can practice dilution-plate calculations with explicit colony, dilution, and volume inputs.
- Laboratory planners can compare plate counts with the 30–300 countable range before selecting a dilution for repeat plating.
- Researchers can estimate original culture concentration and optionally calculate total CFU for a stated sample volume.

## Frequently asked questions

### What is the CFU/mL formula?

CFU/mL = colonies counted × 10ⁿ ÷ plated volume in mL.

### What does the dilution exponent mean?

It is n in 10⁻ⁿ, representing the dilution tube used to seed the plate. For a 10⁻⁶ plate, enter 6.

### What plated volume should I enter for 100 µL?

Enter 0.1 mL because 100 µL equals 0.1 mL.

### What does TNTC mean?

TNTC means too numerous to count. Counts above 300 are flagged and generally call for plating a higher dilution.

### What is the recommended countable range?

The calculator uses 30–300 colonies per plate as the countable range. Counts below 30 may be flagged as too few to count.

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