Plating Dilution Calculator
🧫 Plating Dilution Results
Recommended Dilution for Plating
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Expected Colonies
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at recommended dilution
Number of Steps
—
dilution tubes needed
Sample Volume per Step
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mL to transfer each step
Final Cell Density on Plate
—
CFU/mL after dilution
Serial Dilution Scheme
| Tube | Dilution Factor | Transfer | Diluent | Expected CFU/plate |
|---|
How to Use the Plating Dilution Calculator
Enter your estimated cell density (CFU/mL), the volume you plan to plate, and your preferred dilution step size. The calculator will generate a complete serial dilution scheme and recommend which tube to plate from.
- Cell Density: Your best estimate of starting CFU/mL. Use OD600 or previous counts. Use presets if unsure.
- Volume to Plate: Typically 0.1 mL (100 µL) for spread plates or 1.0 mL for pour plates.
- Dilution Step: 10-fold steps are standard. Use the table to see transfer volumes for each tube.
Plating Dilution Formula
Required Dilution = Target Colonies / (Cell Density × Volume Plated)
Example:
Cell density = 10⁸ CFU/mL, Volume = 0.1 mL, Target = 150 CFU
Required dilution = 150 / (10⁸ × 0.1) = 1.5 × 10⁻⁸
→ Use 10⁻⁷ or 10⁻⁸ dilution tube for plating
Example:
Cell density = 10⁸ CFU/mL, Volume = 0.1 mL, Target = 150 CFU
Required dilution = 150 / (10⁸ × 0.1) = 1.5 × 10⁻⁸
→ Use 10⁻⁷ or 10⁻⁸ dilution tube for plating
Always plate two to three consecutive dilutions to ensure at least one plate falls in the countable 30–300 colony range.
Tips for Accurate Plating
- Plate multiple dilutions: Always plate 2–3 consecutive dilutions as insurance.
- Mix well: Vortex each dilution tube for 5–10 seconds before transferring.
- Spread evenly: Use a sterile glass spreader or loop for uniform colony distribution.
- Count promptly: Count colonies after 16–24 hours to avoid satellite colonies and overgrowth.
- Use fresh diluent: PBS or 0.9% NaCl are standard. Avoid plain water (osmotic stress).