Model stepwise dilutions, plated counts, and estimated original concentration. Enter transfer volumes and steps easily. Build reliable lab dilution workflows with clear calculations today.
This example shows a common tenfold dilution series starting from a dense microbial suspension.
| Step | Transfer (mL) | Diluent (mL) | Total Factor | Dilution Fraction | Estimated Concentration (CFU/mL) |
|---|---|---|---|---|---|
| 1 | 1.0 | 9.0 | 10 | 1.0E-1 | 1.0E7 |
| 2 | 1.0 | 9.0 | 100 | 1.0E-2 | 1.0E6 |
| 3 | 1.0 | 9.0 | 1000 | 1.0E-3 | 1.0E5 |
| 4 | 1.0 | 9.0 | 10000 | 1.0E-4 | 1.0E4 |
| 5 | 1.0 | 9.0 | 100000 | 1.0E-5 | 1.0E3 |
Final Tube Volume: Transfer Volume + Diluent Volume
Step Dilution Factor: Final Tube Volume ÷ Transfer Volume
Total Dilution Factor: (Step Dilution Factor)Number of Steps
Dilution Fraction: 1 ÷ Total Dilution Factor
Final Tube Concentration: Initial Concentration ÷ Total Dilution Factor
Plated Tube Concentration: Colony Count ÷ Plated Volume
Estimated Original Concentration: Plated Tube Concentration × Total Dilution Factor
Microbiology serial dilution helps labs reduce a dense sample into measurable steps. This calculator estimates dilution factors, final tube concentration, plated tube concentration, and the original microbial load. It is useful for colony counting, viable plate work, food testing, water testing, and general biology practice. Clear dilution planning lowers pipetting mistakes and improves repeatability.
Undiluted cultures often contain too many cells to count directly. Serial dilution creates smaller, controlled concentrations across several tubes. A common workflow transfers a fixed sample volume into fresh diluent again and again. Each transfer lowers concentration by a known ratio. When you plate a measured amount, you can count colonies from a countable range and estimate CFU per milliliter in the original sample.
This page uses the transfer volume, diluent volume, and number of steps to find the step dilution factor and total dilution factor. It then estimates the final concentration after the last tube. If you enter a colony count and plated volume, it also back calculates the original concentration. This makes the tool practical for planning dilution series and reviewing plate count results.
Mix each tube well before the next transfer. Use sterile tips and fresh diluent. Label every tube clearly. Plate replicate samples when possible. Avoid plates with very low or very high colony numbers. Record incubation conditions because temperature and time affect growth. Small handling errors can multiply across many steps, so consistency matters throughout the full series.
The step factor shows how much one transfer reduces concentration. The total dilution combines all steps in the series. The dilution ratio is also shown as a fraction of the starting sample. The final tube concentration tells you the expected density before plating. The estimated original concentration uses the plated colony count and plated volume. It assumes each visible colony grew from one viable unit. In real work, clumping and media choice can change the estimate, so compare the result with plate quality and lab notes. Students, technicians, and researchers can all use it for setup checks before running a dilution series.
A serial dilution is a repeated stepwise reduction of sample concentration. Each step uses a known transfer volume and diluent volume. This creates predictable dilution levels for plating, counting colonies, and estimating the original microbial concentration.
They use serial dilutions because many original samples are too concentrated to plate directly. Diluting the sample helps produce countable colonies, improves accuracy, and supports CFU per milliliter estimation from plated results.
The step dilution factor equals final tube volume divided by transfer volume. If you move 1 mL into 9 mL diluent, the final tube volume becomes 10 mL and the step factor becomes 10.
Step dilution describes one transfer event. Total dilution combines all steps in the series. For example, a tenfold step repeated six times produces a total dilution factor of one million.
The calculator first finds concentration in the plated tube using colonies divided by plated volume. It then multiplies that value by the total dilution factor to estimate the original concentration before dilution.
Many labs prefer plates with about 30 to 300 colonies, but protocols differ. Always follow your lab method, organism requirements, and validation rules when selecting a countable plate for calculation.
Yes. The tool uses transfer volume and diluent volume directly, so it can calculate twofold, fivefold, tenfold, or custom serial dilution schemes without changing the formula structure.
No. The estimate depends on observed colonies, plating volume, and the assumed dilution path. Experimental variation, cell clumping, pipetting error, and selective growth conditions can cause differences from the starting value.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.