Calculate dilution factor, final concentration, required volumes, and complete serial dilution tables. Supports C₁V₁=C₂V₂ single-step dilutions, multi-step serial dilutions, and CFU/mL plate count calculations.
✓ Verified: CLSI EP7 Lab Dilution Standards & WHO LQMS Guidelines — April 2026
Enter any three values — the fourth will be calculated automatically.
Required — stock concentrationEnter a valid C₁.
Required — volume taken from stockEnter a valid V₁.
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Enter stock concentration.
e.g. 10 = 1:10 each stepEnter step factor > 1.
1 to 12 stepsEnter 1–12 steps.
Enter aliquot volume.
Enter total tube volume.
Enter aliquot volume.
Enter total final volume.
Enter colony count.
e.g. 0.00001 for 10⁻⁵Enter dilution factor.
Enter plated volume (mL).
Result
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Serial Dilution Table
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Sources & Methodology
🛡️Dilution formulas per CLSI EP7-A3 and WHO Laboratory Quality Management System guidelines.
📋
CLSI EP7-A3 — Interference Testing in Clinical Chemistry
Standard dilution practices for clinical laboratories. clsi.org
🌍
WHO Laboratory Quality Management System (2011)
WHO handbook on dilution protocols for diagnostic labs. who.int
📖
Sambrook & Russell — Molecular Cloning, 4th Ed.
Standard reference for serial dilution preparation in molecular biology.
Example: 1 mL of 1 M into 100 mL total: DF = 100, C₂ = 1M/100 = 0.01 M
Serial 1:10 × 5 steps from 10⁶ CFU/mL: final = 10⁶/10⁵ = 10 CFU/mL
Dilution Factor: The Complete Laboratory Guide
Dilution is one of the most fundamental operations in any chemistry, biology, or clinical laboratory. The key relationship is the dilution equation C₁V₁ = C₂V₂ — moles of solute are conserved during dilution, so the product of concentration and volume is constant before and after. Only the volume changes, reducing the concentration proportionally.
The dilution factor (DF) = V₂/V₁ = C₁/C₂. A DF of 10 (written 1:10) means 1 part sample in 10 total — add 9 parts diluent to 1 part sample. The final concentration equals the initial concentration divided by the dilution factor.
Dilution Factor Reference Table
Notation
DF
Sample
Diluent to Add
Final Conc. from 1 M
1:2
2
1 mL
1 mL
0.500 M
1:5
5
1 mL
4 mL
0.200 M
1:10
10
1 mL
9 mL
0.100 M
1:50
50
0.2 mL
9.8 mL
0.020 M
1:100
100
0.1 mL
9.9 mL
0.010 M
1:1000
1000
10 μL
9.99 mL
0.001 M
Serial Dilution vs Single Dilution
When the required dilution factor is very large (e.g., 10⁶ = 1,000,000x), a single-step dilution requires measuring 1 μL into 1 L — impractical and inaccurate. Serial dilutions chain multiple smaller steps, each using the product of the previous. Six 1:10 steps achieve 10⁶ while only requiring accurate 1 mL transfers at each step.
💡 Notation Warning — Two Meanings of 1:10:
Chemistry/pharmacy: 1 part sample + 9 parts diluent = 10 total (DF = 10)
Some biology: 1 part sample + 10 parts diluent = 11 total (DF = 11)
Always confirm: "1 in 10 total" vs "1 to 10" to avoid errors.
CFU/mL Calculation
After serial dilution, plates with 30–300 colonies give the most statistically reliable counts. CFU/mL = colony count / (dilution factor × volume plated). Example: 47 colonies on a plate inoculated with 0.1 mL from a 10⁻⁵ dilution: CFU/mL = 47 / (10⁻⁵ × 0.1) = 47 / 10⁻₆ = 4.7 × 10⁷ CFU/mL.
Frequently Asked Questions
DF = final volume / aliquot volume = C₁/C₂. DF of 10 means 1 part sample in 10 total (1 mL + 9 mL diluent). Final concentration = initial / DF.
Moles of solute are conserved: C₁=initial conc, V₁=volume taken, C₂=final conc, V₂=total final volume. Rearrange for any unknown. Example: 1 mL of 1 M diluted to 100 mL: C₂ = (1×1)/100 = 0.01 M.
Sequential dilutions where each step uses the product of the previous step. Cumulative DF after n steps = (step DF)ⁿ. Six 1:10 steps achieves 10⁶ = 1,000,000x dilution using only accurate 1 mL transfers.
Dilution factor = total / sample (e.g., DF=10). Dilution ratio = sample:diluent parts (e.g., 1:9). A 1:9 dilution ratio = DF of 10. Always specify notation to avoid ambiguity.
C₂ = C₁ × V₁ / V₂. Example: 1 mL of 5 M into 50 mL total: C₂ = 5 × 1 / 50 = 0.1 M. Or: DF = 50, C₂ = 5M / 50 = 0.1 M.
Add 1 part sample to 9 parts diluent (total = 10 parts, DF = 10). Example: 0.1 mL sample + 0.9 mL diluent = 1.0 mL total. Final concentration = original / 10.
Product of all step factors. Five 1:10 steps: 10⁵ = 100,000. Three 1:2 steps: 2³ = 8. Mixed: DFₜₗₜ̲ = DF₁ × DF₂ × DF₃.
CFU/mL = colonies / (DF × mL plated). Example: 47 colonies, 0.1 mL, DF = 10⁻⁵: CFU/mL = 47 / (10⁻⁵ × 0.1) = 4.7 × 10⁷. Use plates with 30–300 colonies for best accuracy.
1 part sample in 100 total (DF = 100). Prepare: 1 mL sample + 99 mL diluent. Final conc = original / 100.
Large single dilutions require impractically small volumes (e.g., 1 μL into 1 L). Serial steps allow accurate pipetting at each stage, reducing cumulative error. Standard in microbiology, ELISA, and pharmacology.