Each step: transfer 1 mL into 9 mL of diluent, then mix.
| Tube | Dilution | Concentration | Volume left |
|---|---|---|---|
| Stock | 1 | 1 mg/mL | — |
| 1 | 1 : 10 | 0.1 mg/mL | 9 mL |
| 2 | 1 : 100 | 0.01 mg/mL | 9 mL |
| 3 | 1 : 1,000 | 0.001 mg/mL | 9 mL |
| 4 | 1 : 10,000 | 1.000 × 10⁻⁴ mg/mL | 9 mL |
| 5 | 1 : 100,000 | 1.000 × 10⁻⁵ mg/mL | 9 mL |
| 6 | 1 : 1.00000 × 10⁶ | 1.000 × 10⁻⁶ mg/mL | 10 mL |
Use a fresh pipette tip for every transfer and mix each tube thoroughly before taking the next aliquot — carry-over is the most common source of error in serial dilutions.
How it works
Each step moves V ÷ DF of the previous tube into (V − V ÷ DF) of diluent, so every tube ends up with volume V and a concentration DF times lower. After n steps, the total dilution is DFⁿ and the concentration is stock ÷ DFⁿ. Every tube except the last loses one transfer volume when the next aliquot is taken.
You can use any concentration unit — mg/mL, CFU/mL, µM — because only ratios are involved. Small errors compound over many steps, so use calibrated pipettes and a fresh tip each time.
Frequently asked questions
- How do I make a 1:10 serial dilution?
- Put 9 mL of diluent in each tube. Transfer 1 mL of stock into the first tube and mix; then transfer 1 mL of that into the second, and so on. Each tube is ten times more dilute than the one before.
- What is the total dilution after 5 steps of 1:10?
- 10⁵ = 100,000, so a stock of 1 mg/mL becomes 1 × 10⁻⁵ mg/mL (10 ng/mL).
- Why use a serial dilution instead of one big dilution?
- Very large single dilutions need impractically small volumes of stock or huge volumes of diluent. Serial steps keep every pipetted volume measurable and give a whole range of concentrations at once.
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