Tools
Calculators
Each tool shows its formula and a worked example. Always double-check results before use.
Lab
Molarity / mass needed
Practice this topic: Amino acids and proteinsFormula: mass (g) = molarity (M) × volume (L) × molecular weight (g/mol)
Example: 0.5 M NaCl (MW 58.44) in 0.25 L → 0.5 × 0.25 × 58.44 = 7.305 g
C1V1 = C2V2 dilution
Practice this topic: Amino acids and proteinsFormula: V1 = (C2 × V2) / C1 (same units for C1 and C2)
Example: 10× stock to 1× in 50 mL → V1 = 1 × 50 / 10 = 5 mL stock + 45 mL diluent
Percentage solutions
Practice this topic: Amino acids and proteinsFormula: w/v: grams = % × volume (mL) / 100 · v/v: mL solute = % × volume (mL) / 100
Example: 2% w/v agarose in 100 mL → 2 × 100 / 100 = 2 g
Buffer preparation (Henderson–Hasselbalch)
Practice this topic: Amino acids and proteinsFormula: pH = pKa + log([A⁻]/[HA]); ratio r = 10^(pH − pKa); [A⁻] = C·r/(1+r), [HA] = C/(1+r)
Example: 0.1 M phosphate, pH 7.4, pKa 7.21 → r = 1.55; base 0.0608 M, acid 0.0392 M
PCR master mix
Practice this topic: PCR and sequencingFormula: Per-reaction volume × (reactions + 10% extra). Defaults for a 25 µL reaction.
Example: 10 reactions → 11 × 12.5 µL 2× mix = 137.5 µL; 11 × 1 µL each primer; water to volume
Cell seeding density
Practice this topic: Cell and tissue cultureFormula: Volume of suspension = (density × area × wells) / cell concentration
Example: 1×10⁴ cells/cm², 9.5 cm² well (6-well), 6 wells, 5×10⁵ cells/mL → 1.14 mL
Unit converter
Formula: value × (factor of from-unit / factor of to-unit), within mass, volume or concentration
Example: 250 µL → mL = 250 × 10⁻⁶ / 10⁻³ = 0.25 mL
Sequences
DNA/RNA concentration (A260)
Practice this topic: UV-Vis spectroscopyFormula: Concentration (ng/µL) = A260 × dilution factor × factor (dsDNA 50, RNA 40, ssDNA 33)
Example: A260 0.25, 1:10 dilution, dsDNA → 0.25 × 10 × 50 = 125 ng/µL
GC content & reverse complement
Practice this topic: Sequence alignmentFormula: GC% = (G + C) / length × 100; reverse complement: reverse, then A↔T(U), G↔C
Example: ATGCGC → GC 66.7%, reverse complement GCGCAT
Pharmacy
For education only, not for clinical decisions.
Basic dose calculator
For education only, not for clinical decisions.
Practice this topic: Clinical calculationsFormula: Dose (mg) = dose per kg (mg/kg) × weight (kg); volume (mL) = dose / concentration (mg/mL)
Example: 10 mg/kg for 20 kg, syrup 125 mg/5 mL (25 mg/mL) → 200 mg = 8 mL
Alligation
For education only, not for clinical decisions.
Practice this topic: Clinical calculationsFormula: Parts of higher = desired − lower; parts of lower = higher − desired
Example: Make 100 g of 10% from 20% and 5% → 5 parts 20% : 10 parts 5% = 33.3 g + 66.7 g
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