Plaque Forming Units Calculator (PFU/mL)

Plaque Forming Units Calculator (PFU/mL) | Online Free Tool | Elysia Tools

Tool usage guide

Learn when to use this tool, what it supports, and how real users apply it.

Key facts

Category: Health
Input types: textarea, number
Output type: json
Sample coverage: 4
API ready: Yes

Overview

The Plaque Forming Units Calculator converts plaque-assay counts into PFU/mL titer. Enter one or more plate counts, the fold-dilution of the plated sample, and the volume plated in microliters to obtain mean titer, multi-plate statistics, and 30–300 counting-range warnings.

When to use

After counting plaques on double-layer agar plates from a serial dilution.
When averaging replicate plates at the same dilution to report a stock titer.
When checking whether mean plaque counts fall in the reliable 30–300 range before calculating PFU/mL.

How it works

1Enter plaque counts from each plate, separated by commas, spaces, or new lines.
2Enter the fold-dilution of the plated sample (for example 1000000 for a 10⁻⁶ dilution) and the plated volume in µL (100 µL is typical).
3The tool averages the counts, converts plated volume to mL, and computes PFU/mL = mean plaques × dilution factor ÷ volume in mL.
4It reports standard deviation, CV%, and warns if the mean count is below 30 or above 300.

Use cases

Bacteriophage enumeration after serial dilution and double-layer agar plating.
Viral plaque-assay titer calculations in a teaching or research lab.
Checking replicate-plate agreement and counting-range validity before reporting PFU/mL.

Examples

1. Replicate plates at 10⁻⁶ dilution

Phage lab technician

Background

Two plates from a 10⁻⁶ dilution of a bacteriophage stock were counted after overnight incubation.

Problem

Convert the counts into stock titer in PFU/mL and check plate-to-plate consistency.

How to use

Enter plaque counts 112 and 104, dilution factor 1000000, and plated volume 100 µL.

plaqueCounts: 112, 104
dilutionFactor: 1000000
platedVolumeUl: 100

Outcome

Mean 108 plaques (SD 5.66, CV 5.24%). Titer ≈ 1.08 × 10⁹ PFU/mL with no counting-range warning.

2. Overcrowded plate with TNTC warning

Virology student

Background

One plate from a 10⁻⁴ dilution received 200 µL of sample and showed 312 plaques.

Problem

Obtain a titer estimate while being alerted that the count is outside the reliable range.

How to use

Enter plaque count 312, dilution factor 10000, and plated volume 200 µL.

FAQ

How is PFU/mL calculated?

PFU/mL = mean plaque count × dilution factor ÷ plated volume in mL. Volume entered in µL is divided by 1000.

Can I use counts from more than one plate?

Yes. List one number per plate. The calculator uses the mean and reports SD and CV%.

What do the 30–300 warnings mean?

A mean below 30 is statistically less reliable; a mean above 300 often means plaques merged and the titer is underestimated. Use a less or more dilute sample.

What value do I enter for dilution factor?

The fold-dilution of the sample that was actually plated relative to the original stock. A 10⁻⁶ dilution is entered as 1000000.

What plated volume should I use?

The volume of diluted sample mixed into the top agar, in microliters. 100 µL is a common default.

plaqueCounts: 312
dilutionFactor: 10000
platedVolumeUl: 200

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Continue with connected tools and hubs

Learn when to use this tool, what it supports, and how real users apply it.

Key facts

Overview

When to use

How it works

Use cases

Examples

1. Replicate plates at 10⁻⁶ dilution

2. Overcrowded plate with TNTC warning

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