Biomath calculators
Free molecular-biology calculators that run entirely in your browser: nucleic-acid mass and mole conversions, ligation ratios, absorbance-to-concentration, dilutions and molarity. Every page shows the formula with its citation, a worked example, and the reference calculators the results are verified against.
No account needed. For calculations on your actual sequences — digests, primers, assemblies — the full workbench is free too.
/ DNA conversions
dsDNA mass ↔ moles converter
Convert double-stranded DNA between micrograms and picomoles from fragment length.
pmol = µg × 10⁶ / (N bp × 660)
ssDNA (oligo) concentration converter
Convert single-stranded DNA and oligo concentrations between µg/ml and pmol/µl from oligo length, using 330 g/mol per nucleotide.
pmol/µl = (µg/ml) × 10³ / (N nt × 330)
Linear DNA ends calculator
Convert micrograms of linear double-stranded DNA to picomoles of ends for ligation, labelling and phosphatase reactions.
pmol ends = 2 × µg × 10⁶ / (N bp × 660)
Ligation calculator (insert : vector)
Calculate how many ng of insert to add to a ligation from vector mass, vector and insert lengths, and the desired insert:vector molar ratio.
ng insert = ng vector × (insert kb / vector kb) × (insert:vector molar ratio)
OD260 concentration calculator
Convert an A260 absorbance reading to nucleic acid concentration: dsDNA ×50, RNA ×40, ssDNA ×33 µg/ml per OD unit, with dilution factor.
c (µg/ml) = A260 × factor × dilution (dsDNA 50, RNA 40, ssDNA 33)
/ Oligos & sequences
Oligo melting temperature (4 methods)
Calculate oligo melting temperature four ways side by side: Wallace rule, GC-content formula, salt-adjusted, and SantaLucia 1998 nearest-neighbor thermodynamics with salt and concentration inputs.
Tm = ΔH × 1000 / (ΔS + 0.368·(N−1)·ln[Na⁺] + R·ln(Cₜ/4)) − 273.15
GC content calculator
Calculate GC content and full base composition of any DNA sequence: %GC = (G+C)/length × 100.
%GC = (G + C) / N × 100
Reverse complement calculator
Generate the reverse complement, complement and reverse of any DNA sequence with full IUPAC ambiguity code support.
revcomp(s) = reverse(complement(s)), A↔T · G↔C · R↔Y · K↔M · B↔V · D↔H · S,W,N ↔ themselves
Oligo extinction coefficient (ε260)
Calculate an oligo's extinction coefficient at 260 nm by the nearest-neighbor method (Cavaluzzi & Borer 2004), plus concentration from A260, nmol per OD and µg per OD.
ε260 = Σ ε(dinucleotides) − Σ ε(internal monomers) · c (µM) = A260 × 10⁶ / ε
Oligo self-complementarity check
Scan an oligo for self-dimers, 3′-anchored primer-dimers and hairpins by sliding self-alignment (OligoCalc method).
Slide seq vs revcomp(seq) at every offset → longest complementary run; hairpin: inverted repeat, stem ≥ 4, loop ≥ 3
/ Protein
DNA coding capacity calculator
Convert DNA length to protein coding capacity: codons = bp/3, minus the stop codon, at ~110 Da per residue.
codons = ⌊bp / 3⌋ · residues = codons − 1 (stop) · protein kDa ≈ residues × 110 / 1000
Protein mass ↔ moles converter
Convert protein between micrograms and picomoles from molecular weight in kDa, plus the number of molecules: pmol = µg × 1000 / kDa.
pmol = µg × 10³ / kDa · µg = pmol × kDa / 10³ · molecules = pmol × 6.022 × 10¹¹
Protein concentration from A280
Convert an A280 absorbance reading to protein concentration in mg/ml and µM using the extinction coefficient: mg/ml = A280 × MW / ε.
c (mg/ml) = A280 × MW / ε · c (µM) = A280 / ε × 10⁶
/ Solutions & buffers
Dilution calculator (C₁V₁ = C₂V₂)
Solve C₁V₁ = C₂V₂ for stock volume, stock concentration, final concentration or final volume.
C₁V₁ = C₂V₂ → V₁ = C₂ × V₂ / C₁
Molarity calculator
Calculate the mass of compound to weigh for a solution of known molarity and volume: mass = molarity × volume × formula weight.
mass (g) = molarity (mol/L) × volume (L) × formula weight (g/mol)
Serial dilution planner
Plan a serial dilution: per-step diluent and transfer volumes for any fold factor and number of steps.
diluent per step = V_transfer × (fold − 1) · total dilution = foldⁿ
/ PCR & qPCR
PCR annealing temperature calculator
Calculate the optimal PCR annealing temperature from primer Tm values: the Tm − 5 °C rule and the Rychlik 1990 formula Ta = 0.3·Tm(primer) + 0.7·Tm(product) − 14.9.
Ta = 0.3·Tm(lower primer) + 0.7·Tm(product) − 14.9
DNA copy number calculator
Convert DNA mass to molecule copies for qPCR standard curves: copies = ng × 6.022×10²³ / (bp × 660 × 10⁹).
copies = ng × 6.022×10²³ / (N bp × 660 × 10⁹)
qPCR efficiency calculator
Calculate qPCR amplification efficiency from your standard-curve slope: E = 10^(−1/slope) − 1.
E = 10^(−1/slope) − 1 · % efficiency = 100 × E · slope −3.32 ⇒ 100%
PCR master mix calculator
Scale a PCR recipe to any number of reactions with pipetting overage: each component = per-reaction volume × reactions × (1 + overage).
component volume = per-reaction volume × reactions × (1 + overage)
/ Cell culture
Cell doubling time calculator
Calculate cell population doubling time from two counts and the elapsed time: Td = t × ln2 / ln(Nt/N0).
Td = t × ln 2 / ln(Nₜ/N₀)
Cell seeding density calculator
Calculate cells to seed from target density and vessel growth area (96-well to T-175, Corning areas), plus the stock volume needed.
cells = density (cells/cm²) × growth area (cm²) · volume = cells / stock (cells/ml)
Transformation efficiency calculator
Calculate bacterial transformation efficiency in CFU/µg from colonies counted, DNA amount, recovery volume, plated volume and dilution.
CFU/µg = colonies × dilution × (V_recovery / V_plated) / µg DNA
/ General lab
Temperature converter (°C ↔ °F)
Convert between Celsius, Fahrenheit and Kelvin with the exact formulas, plus a reference table of standard lab temperatures: 37 °C incubation, 72 °C extension, −80 °C storage.
°F = °C × 9/5 + 32 · °C = (°F − 32) × 5/9 · K = °C + 273.15
Agarose gel percentage guide
Pick the right agarose percentage for your DNA fragment sizes: 0.5% for 1–30 kb down to 2% for 50 bp–2 kb, per standard electrophoresis references.
0.5% → 1–30 kb · 0.7% → 0.8–12 kb · 1.0% → 0.5–10 kb · 1.2% → 0.4–7 kb · 1.5% → 0.2–3 kb · 2.0% → 0.05–2 kb
g-force ↔ RPM converter
Convert between centrifuge RPM and relative centrifugal force: RCF = 1.118×10⁻⁵ × radius(cm) × RPM².
RCF = 1.118 × 10⁻⁵ × r (cm) × RPM² · RPM = √(RCF / (1.118 × 10⁻⁵ × r))
/ In-app analysis tools
Need this on a real construct?
The Talindrew workbench runs digests, primer design and assemblies on your own sequences — free.