Lab Calculators

Bench arithmetic without the spreadsheet. In cards 1 and 2, pick which quantity to solve for; everything recalculates as you type.

1Mass · volume · concentration

Mass

Molecular weight (g/mol)

Volume

Concentration

n = m / MW, C = n / V. Tick the quantity you want and fill in the other three.

2Dilution C₁V₁ = C₂V₂

Stock concentration C₁

Stock volume V₁

Final concentration C₂

Final volume V₂

Also gives the dilution factor and the diluent to add. For DMSO stocks, keep the final DMSO percentage in mind (shown when C₁ ≥ 1 mM).

3Serial dilution series

Top concentration

Dilution factor

Number of points

Volume per well/tube (final)

Each step transfers V/(f−1) of the previous tube into V of diluent (so the last tube ends with the same volume after transfer). Prepare the top tube with a little extra.

4Stock solution from powder

Target concentration

Volume

Molecular weight (g/mol)

Purity / content (%)

Or: mass actually weighed → volume of solvent to add

m = C · V · MW / (purity/100). For salts or hydrates use the MW of the form you weigh.

5Percent, ppm and molar

% w/v (g per 100 mL)

Molecular weight (g/mol)

1 % w/v = 10 mg/mL = 10 g/L · 1 ppm ≈ 1 mg/L (dilute aqueous) · M = (g/L) / MW. The default is physiological saline.

6Dose by body weight

Dose (mg/kg)

Body weight (kg)

Dosing solution concentration

Number of animals / doses (for total stock)

Default is a 25 g mouse at 10 mg/kg from a 1 mg/mL solution (0.25 mg → 250 µL, i.e. 10 mL/kg). Prepare ~20 % extra for dead volume.

7Buffer (Henderson–Hasselbalch)

pKa

Target pH

Total buffer concentration

Volume

MW of acid form (optional)

MW of base form (optional)

pH = pKa + log([A⁻]/[HA]). Defaults: phosphate (pKa 7.21) at pH 7.4 from NaH₂PO₄ / Na₂HPO₄ (anhydrous). Useful range ≈ pKa ± 1; adjust with acid/base at the end.