How It Works
This planner works in 4 steps.
Define drug A (rows)
Type the top concentration, factor, and number of rows.
Define drug B (columns)
Type the top concentration, factor, and number of columns.
Set the well volume
Type the final well volume and the share contributed by each drug.
Read the plate map
The planner returns each well's pair, the 2× or 4× stocks, and the single-drug control lanes.
The Formula
The formula sets each well from the row concentration of drug A and the column concentration of drug B.
(A_r, B_c) = (A₀ / F_Aʳ, B₀ / F_Bᶜ)C_stock = C_final × 2FICI = MIC_A,comb / MIC_A,alone + MIC_B,comb / MIC_B,alone- A₀ / B₀:
- Top concentrations
- F_A / F_B:
- Step factors
- r / c:
- Row and column index
- MIC:
- Minimum inhibitory concentration
Drug A at 64 µg/mL in row A halves to 0.5 µg/mL in row H. Drug B at 32 µg/mL in column 1 halves across 11 columns. Adding 50 µL of each 2× stock gives the final pair in 100 µL.
Conversion Table
The conversion table shows a twofold checkerboard with drug A down rows A to H and drug B across columns 1 to 11.
| Row | Drug A | Drug B | Control lane |
|---|---|---|---|
| A | Drug A 64 µg/mL | Columns 1–11: Drug B 32 → 0.03 µg/mL | Column 12: Drug A alone |
| B | Drug A 32 µg/mL | Columns 1–11: Drug B 32 → 0.03 µg/mL | Column 12: Drug A alone |
| C | Drug A 16 µg/mL | Columns 1–11: Drug B 32 → 0.03 µg/mL | Column 12: Drug A alone |
| D | Drug A 8 µg/mL | Columns 1–11: Drug B 32 → 0.03 µg/mL | Column 12: Drug A alone |
| E | Drug A 4 µg/mL | Columns 1–11: Drug B 32 → 0.03 µg/mL | Column 12: Drug A alone |
| F | Drug A 2 µg/mL | Columns 1–11: Drug B 32 → 0.03 µg/mL | Column 12: Drug A alone |
| G | Drug A 1 µg/mL | Columns 1–11: Drug B 32 → 0.03 µg/mL | Column 12: Drug A alone |
| H | Drug A 0.5 µg/mL | Columns 1–11: Drug B 32 → 0.03 µg/mL | Column 12: Drug A alone |
What Is the Checkerboard Dilution Planner?
The Checkerboard Dilution Planner is a tool that arranges 2 independent concentration series at right angles on a plate, so every well holds a unique pair of concentrations. One drug varies down the rows and the other varies across the columns.
Checkerboard assays test drug combinations for synergy, additivity, or antagonism. The fractional inhibitory concentration index (FICI) sums each drug's MIC in combination divided by its MIC alone. Many studies read FICI ≤ 0.5 as synergy, per the interpretation the user's protocol adopts. The planner returns the well map, the 2× stock concentrations needed when 2 equal volumes are combined, and an FICI worksheet.
Common Uses
There are 5 main uses of this planner.
Antibiotic synergy
Microbiologists test 2-antibiotic combinations against isolates.
Cancer drug pairs
Oncology labs test combination effects on cell viability.
Capture and detection antibody pairing
Assay developers titrate both ELISA antibodies at once.
Adjuvant screens
Researchers test potentiators with existing drugs.
Cytokine interactions
Immunologists test 2 stimuli across concentration grids.