Antibiotic Dilution Calculator
Calculate antibiotic dilution with our free science calculator. Uses standard scientific formulas with unit conversions and explanations.
Formula
C1 x V1 = C2 x V2 (therefore V1 = C2 x V2 / C1)
C1 is the stock (initial) concentration, V1 is the volume of stock needed, C2 is the desired final concentration, and V2 is the desired final volume. The volume of solvent (diluent) to add equals V2 - V1. The dilution factor equals C1/C2.
Frequently Asked Questions
What is the C1V1 = C2V2 dilution formula?
The C1V1 = C2V2 equation is the fundamental dilution formula used in laboratory science. C1 is the initial (stock) concentration, V1 is the volume of stock solution needed, C2 is the desired final concentration, and V2 is the desired final volume. This equation works because the amount of solute (antibiotic) remains constant before and after dilution. For example, if you have a 1000 ug/mL stock and need 10 mL at 50 ug/mL: V1 = (50 x 10) / 1000 = 0.5 mL of stock solution, then add 9.5 mL of solvent to reach 10 mL total volume.
How do I prepare antibiotic stock solutions?
To prepare antibiotic stock solutions, first check the solubility of the antibiotic in your chosen solvent (water, DMSO, ethanol, etc.). Weigh the appropriate amount using an analytical balance and dissolve in the solvent. Stock solutions are typically prepared at 1000x the working concentration. For example, if your working concentration is 100 ug/mL, prepare a stock at 100 mg/mL. Filter-sterilize using a 0.22 um syringe filter if the antibiotic is heat-sensitive. Aliquot into single-use volumes to avoid repeated freeze-thaw cycles, and store at -20C or as recommended by the manufacturer.
What are common antibiotic working concentrations?
Common working concentrations for laboratory antibiotics vary by application. For bacterial selection in molecular biology: ampicillin 100 ug/mL, kanamycin 50 ug/mL, chloramphenicol 25-34 ug/mL, tetracycline 10 ug/mL, gentamicin 10 ug/mL, and streptomycin 50 ug/mL. For cell culture: penicillin 100 U/mL with streptomycin 100 ug/mL (Pen-Strep), gentamicin 50 ug/mL, and puromycin 1-10 ug/mL for selection. MIC testing uses a range of concentrations typically from 0.06 to 128 ug/mL in 2-fold serial dilutions.
How do I account for antibiotic potency in dilutions?
Antibiotic potency (or purity) must be factored into stock solution preparation. Manufacturers report potency as the active fraction of the total weight, typically expressed as ug of active compound per mg of powder. If an antibiotic has a potency of 850 ug/mg (85%), you need to weigh more powder to achieve the desired concentration. The adjusted weight = desired weight / (potency/1000). For example, to prepare 10 mL of 100 mg/mL ampicillin at 90% potency: weight needed = (100 x 10) / 0.90 = 1,111 mg instead of 1,000 mg. Always check the certificate of analysis for the exact potency of your lot.
How does the dilution formula work?
The dilution formula is C1V1 = C2V2, where C is concentration and V is volume. If you have 100 mL of 2M HCl and need 0.5M, solve: 2 x 100 = 0.5 x V2, so V2 = 400 mL total volume. Add 300 mL of water to 100 mL of stock solution. Always add acid to water, never the reverse.
Can I use Antibiotic Dilution Calculator on a mobile device?
Yes. All calculators on NovaCalculator are fully responsive and work on smartphones, tablets, and desktops. The layout adapts automatically to your screen size.