How It Works
This calculator works in 4 steps.
Enter the calculated volume
Type V₁ from a dilution calculation, or the stock, target, and final volume.
Enter the pipette increment
Type the dial step, such as 0.02, 0.2, or 2 µL.
Round the volume
The calculator rounds to the nearest increment.
Read the actual concentration
The calculator returns C₂ for the rounded volume and the percent difference from plan.
The Formula
The formula rounds the volume to the nearest increment and reapplies C₂ = C₁V₁ / V₂.
V_r = round(V₁ / i) × iC_actual = C₁ × V_r / V₂% dev = 100 × (C_actual − C₂) / C₂- V₁:
- Calculated volume
- i:
- Pipette increment
- V_r:
- Rounded volume
- C_actual:
- Concentration delivered
A target of 0.237 mM from 10 mM in 100 µL gives V₁ = 2.37 µL. Rounded to 2.4 µL, the actual concentration is 0.24 mM, a deviation of +1.27%.
Conversion Table
The conversion table rounds 5 calculated volumes and shows the actual concentration and deviation (shared concentration unit).
| Calculated volume | Increment | Rounded volume | Planned C₂ | Actual C₂ | Deviation |
|---|---|---|---|---|---|
| 2.37 µL | 0.1 µL | 2.4 µL | 0.237 | 0.24 | 1.27% |
| 3.33 µL | 0.1 µL | 3.3 µL | 0.333 | 0.33 | -0.901% |
| 2.5 µL | 0.2 µL | 2.6 µL | 2.5 | 2.6 | 4% |
| 2.26 µL | 0.2 µL | 2.2 µL | 1.13 | 1.1 | -2.65% |
| 33.7 µL | 1 µL | 34 µL | 3.37 | 3.4 | 0.89% |
What Is the Pipette Increment Rounding Calculator?
The Pipette Increment Rounding Calculator is a tool that rounds a calculated transfer volume to the nearest setting a pipette can dial and recalculates the concentration the rounded volume produces. The tool reports the percent difference between the planned and actual concentration.
Adjustable pipettes move in fixed steps. A typical P20 dials in 0.02 µL steps, a P200 in 0.2 µL steps, and a P1000 in 2 µL steps. A calculated 2.37 µL becomes 2.4 µL on a P20 set to 0.1 µL display precision. The calculator records the actual concentration, so the label and data match the real solution.
Common Uses
There are 5 main uses of this calculator.
Label accuracy
Users print the actual, not planned, concentration.
Data correction
Analysts use the actual concentration in calculations.
Tolerance checks
QC staff confirm the deviation falls within method limits.
SOP rounding rules
SOP writers set rounding rules for each pipette.
Training
Trainers show how rounding moves concentration.