Starlight Tools

Serial Dilution Calculator and Planner

Create a bench-ready serial dilution protocol for stock to target work, a 10-fold dilution ladder, or a concentration range. Enter the dilution method, volumes, replicates, and overfill allowance to calculate transfer volumes, diluent volumes, and total reagent needs.

Inputs

Stock, target, and tube concentrations must use the same family.

Used in the protocol wording.

Defaults to diluent if left blank.

Examples: Tube, Well A, Standard.

This is Tube 1 concentration, not automatically divided again.

Use 10 for 1:10, 2 for a two-fold standard curve.

Includes Tube 1.

If higher than Tube 1, the protocol adds a stock-to-first-tube step.

Volume planning

Volume retained for each assay, plate, or working dilution.

Minimum volume is multiplied by this count.

Percent extra for overfill, wetting, and pipetting loss.

Inline warnings show when transfer volumes are outside this range.

Dilution protocol

Overview
Overall dilution \(D=C_\mathrm{stock}/C_\mathrm{target}\): —
Steps: —
Factors: —
Volumes
Minimum per dilution—
Total stock used—
Total diluent—
Step-by-step protocol
Choose a preset or enter values to generate protocol steps.
Calculation table
—
Notes

Formulas used by the calculator

Total dilution factor

\(D = C_\mathrm{start}/C_\mathrm{target}\). For serial steps, \(D = f_1 \times f_2 \times ... \times f_n\).

Transfer volume

\(V_\mathrm{transfer} = V_\mathrm{total}/f\). A 10-fold 1 mL dilution transfers 100 µL.

Diluent volume

\(V_\mathrm{diluent} = V_\mathrm{total} - V_\mathrm{transfer}\). For 1 mL at 10-fold, add 900 µL diluent.

Cumulative dilution

\(C_i = C_0/(f_1 \times ... \times f_i)\). Each tube concentration follows the product of previous folds.

Range-derived fold

\(f = (C_\mathrm{start}/C_\mathrm{end})^{1/n}\), where \(n\) is the number of dilution steps.

Minimum volume

\(V_\mathrm{min} = V_\mathrm{use} \times \mathrm{replicates} \times (1+\mathrm{allowance})\).

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 three methods. Dilution factor builds a fixed-fold ladder, such as a 10-fold dilution across eight tubes. Concentration range derives the per-step fold from your first concentration, final concentration, and desired number of dilution steps. Stock to target splits a large stock-to-working dilution into practical smaller steps.

To use the calculator, choose the method that matches your protocol, then enter the concentration values, volume needed per dilution, replicate count, and dead-volume allowance. If you have pipette limits, enter the minimum and maximum transfer volume so the plan flags impractical steps. The output lists each tube or well label, transfer volume, diluent volume, resulting concentration, and a plain-language dilution protocol.

  • Step 1: Choose dilution factor, concentration range, or stock to target.
  • Step 2: Enter concentrations and the number of tubes or dilution steps.
  • Step 3: Add volume per dilution, replicates, overfill, and pipette limits.
  • Step 4: Review the protocol, calculation table, total stock used, and total diluent needed.

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.

Practical worked examples

1:10 serial dilution in 1 mL tubes

Add 900 µL diluent to Tube 2, transfer 100 µL from Tube 1, mix, then repeat. The calculator uses the same \(V_\mathrm{transfer}=V_\mathrm{total}/10\) relationship for every 10-fold step.

2-fold standard curve in a 96-well plate

Prepare the highest standard in Well A1, then transfer half the working volume through the series. Replicates increase the minimum volume retained in each well or reservoir.

Stock-to-working antibody dilution

For a 1 mg/mL antibody stock to a 1 µg/mL working solution, stock-to-target mode breaks the 1000× dilution into practical steps and reports total PBS or buffer needed.

CFU/mL plating workflow

A 10-fold ladder plus 100 µL plating volumes documents which tube produced countable colonies and keeps enough extra volume for repeat plates.

How to prepare a serial dilution

  1. Label tubes or wells in order, using the same labels shown in the protocol output.
  2. Add the calculated diluent volume to the receiving tube first.
  3. Transfer the calculated sample volume from the stock or previous tube.
  4. Mix thoroughly using the method specified by your lab SOP.
  5. Repeat the add, transfer, and mix sequence until the final dilution is prepared.

Serial dilution FAQ

How do I make a 1:10 serial dilution?

Add nine parts diluent and one part sample. For a 1 mL tube, add 900 µL diluent, transfer 100 µL sample, then mix before the next step.

What is the difference between dilution factor and dilution ratio?

Dilution factor is total volume divided by transferred sample volume. A dilution ratio may be written as sample:diluent or sample:total, so confirm the convention before pipetting.

How much do I transfer for a 10-fold dilution?

Use \(V_\mathrm{transfer}=V_\mathrm{total}/10\). For 1000 µL total, transfer 100 µL and add 900 µL diluent.

How many tubes do I need?

Fixed-factor ladders need one tube per concentration. Stock-to-target plans use as many steps as needed to stay within the selected fold and pipette constraints.

How do replicates change volume?

Replicates multiply the retained volume needed at each dilution. The calculator also reserves transfer volume for the next tube.

Should I include overfill?

Yes for most bench workflows. A 5% to 15% allowance helps cover wetting, evaporation, and pipetting loss; regulated work should follow the lab SOP.

Calculation assumptions and review

Last updated

June 30, 2026. Page calculations use visible formulas and client-side JavaScript.

Formula basis

Serial dilution steps use conservation of concentration ratio: \(C_1V_1=C_2V_2\), dilution factor products, and unit conversions within a single concentration family.

Unit assumptions

Molar units convert through M, mM, and µM. Mass/volume units convert through µg/mL equivalents. Count units convert through CFU/mL. Stock and target units must stay in the same family.

Privacy and lab safety

Inputs stay in your browser. Follow your lab SOPs for hazardous, clinical, sterile, regulated, or diagnostic work.

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