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Pharmaceutical Calculators

Serial Dilution Calculator

Calculate the concentration, stock volume, and diluent volume at every step of a serial dilution series. Supports 1:2, 1:5, 1:10, 1:100, and custom dilution ratios.

Formula
Cn = C0 × Dn
C0 = Initial stock concentration    D = Dilution factor per step
n = Step number    Cn = Concentration at step n
Each step: Cn = C(n-1) × D
Enter Values
Starting Concentration
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Total Dilution Factor
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×
Final Concentration
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Step Dilution Concentration Stock Volume Diluent Volume

How to Use

1
Enter the starting concentration of your stock solution (C0) and select the unit (mg/mL, μg/mL, CFU/mL, or mol/L).
2
Select the dilution ratio for each step — 1:2, 1:5, 1:10, 1:100, or enter a custom ratio.
3
Enter the number of dilution steps you want to calculate (1 to 12).
4
Enter the total volume to prepare at each step and choose your volume unit.
5
Click Calculate to see the full concentration table with stock and diluent volumes for every step.

Worked Example

Example: 3-Step 1:10 Serial Dilution

Starting with 1 mg/mL, making 3 serial 1:10 dilutions with 1 mL total volume per step:

Step 1: 0.1 mg/mL — take 0.1 mL of stock + add 0.9 mL diluent

Step 2: 0.01 mg/mL — take 0.1 mL of Step 1 solution + add 0.9 mL diluent

Step 3: 0.001 mg/mL — take 0.1 mL of Step 2 solution + add 0.9 mL diluent

Total dilution factor after 3 steps: 1000×

About Serial Dilution

Serial dilution is a technique in which a solution is progressively diluted in a stepwise manner, with each step using the output of the previous step as its starting material. This allows scientists to create a wide range of concentrations — spanning multiple orders of magnitude — from a single stock solution using only a few pipetting steps.

In pharmaceutical and clinical laboratories, serial dilution is the foundation of calibration curve preparation for quantitative assays (HPLC, ELISA, PCR), antimicrobial susceptibility testing (MIC/MBC determination), cell viability counting (colony-forming units), and pharmacokinetic sample analysis.

The key formula is Cn = C0 × Dn, where D is the per-step dilution factor (e.g., 0.1 for a 1:10 dilution). Because errors from pipetting and measurement accumulate with each step, it is important to use calibrated micropipettes and to mix thoroughly between steps.

For simple one-step dilutions, use the Dilution Calculator.

Frequently Asked Questions

Serial dilution is used in pharmaceutical and clinical laboratory settings to create precise concentration series for calibration curves (HPLC, ELISA), minimum inhibitory concentration (MIC) testing, cell counting and viability assays, drug potency testing, and preparation of standard reference solutions. Each step reduces concentration by a fixed factor, enabling a wide dynamic range with only a few dilutions.
In a serial dilution, each step dilutes the product of the previous step — errors can accumulate across steps. In a parallel dilution, all concentrations are prepared independently and directly from the original stock solution. Serial dilution is more efficient for creating many points over a wide range, while parallel dilution offers greater accuracy per point because errors do not compound.
For a 1:10 serial dilution, take 1 part of the current solution and add 9 parts of diluent. The concentration reduces by 10× at each step. For a 1 mL total volume: take 0.1 mL of sample and add 0.9 mL diluent. The dilution factor D = 0.1, and the concentration formula is Cn = C0 × (0.1)n.
The formula is: Cn = C0 × Dn, where C0 is the initial stock concentration, D is the dilution factor per step (e.g., 0.1 for 1:10), and n is the step number. For each individual step: Cn = C(n-1) × D, meaning each step multiplies the previous concentration by the dilution factor.
For a reliable calibration curve, typically 5–7 concentration points are used, spanning 2–3 orders of magnitude (100× to 1000× total dilution range). FDA and ICH Q2(R1) guidelines require at least 5 non-zero calibration levels for quantitative bioanalytical assays. For HPLC methods, 6 levels covering the expected sample concentration range is standard practice.

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