Lab Dilution Planner — Serial Dilutions

Worked examples

Auto (antibody): Stock 1 mg/mL → target 1 µg/mL, final 10 mL, step volume 1 mL, limits 2–1000 µL, snap common. A 10× then 100× plan is typical; final tube is prepared to the working volume with ~10% overfill.

Ladder: 10-fold, 8 tubes, 1 mL per tube → transfer 100 µL, add 900 µL diluent each step.

How this planner works

This serial dilution planner turns a target concentration into a clear, step-by-step mixing plan. A serial dilution is a sequence of smaller dilutions that together reach a large overall dilution factor. Instead of trying to pipette a tiny volume all at once, you make a series of manageable transfers with a consistent total volume in each tube. That approach is common in microbiology, biochemistry, and clinical labs because it is more accurate and easier to reproduce.

The key idea is the dilution factor. If your stock concentration is \(C_s\) and your target is \(C_t\), the total dilution factor is \(D = C_s/C_t\). The planner then splits that overall factor into smaller step factors that are practical for pipetting. Each step uses a transfer volume and a diluent volume that add up to your chosen total volume per tube, so the concentration drops in a predictable way at every stage.

There are two modes. Auto searches for a short series of friendly step factors that multiply to the total dilution. It respects your minimum and maximum transfer limits, and it can adjust the final step so you hit the target exactly. Ladder uses a fixed fold (for example, 10-fold) across a set number of tubes, which is useful for standard curves or plate counts where each tube should be the same fold-change from the previous one.

To use the calculator, start by entering your stock concentration and target concentration, then choose a final volume and a per-step total volume. If you have pipette limits, enter the minimum and maximum transfer volume so the plan stays within realistic lab constraints. Select Auto if you want the tool to design the steps, or choose Ladder if you already know the fold per tube. The output lists each tube, the transfer volume, the diluent volume, and the resulting concentration.

• Step 1: Enter stock and target concentrations (for example, mg/mL to µg/mL).
• Step 2: Set the final volume and the per-tube total volume.
• Step 3: Add transfer limits if you want to avoid tiny or overly large pipetting steps.
• Step 4: Choose Auto or Ladder, then review the tube-by-tube plan.

Typical use cases include preparing antibiotic dilutions, making a protein standard series for a Bradford assay, diluting DNA for qPCR, or building a calibration curve for spectroscopy. If you are counting colonies, a 10-fold ladder makes it easy to estimate CFU/mL from plate counts. The planner saves time, reduces errors, and documents a repeatable dilution scheme.

Sanity check: the product of all step factors should equal \(D\). If it doesn’t, the tool won’t accept the plan.