Lab calculation guides

Step-by-step explanations of the calculations behind common bench work, each with a worked example and a calculator that does it for you.

Reference

• Molecular weights of common lab chemicals

  Searchable table of 57 reagents with one-click molarity calculation.

Guides

• How to pool NGS libraries at equal molarity

  Convert library concentrations from ng/µL to nM and pool Illumina libraries equimolarly, with a worked example and common pitfalls.

• How to calculate a PCR master mix

  Work out the volume of each PCR component per reaction and scale it to a master mix with overage, with a worked 25 µL example.

• How to calculate qPCR fold change with the ΔΔCt method

  Step-by-step ΔΔCt (2^-ΔΔCt) calculation for relative gene expression, with a worked example, replicate handling and when to use Pfaffl instead.

• How to calculate primer Tm and annealing temperature

  Compare the Wallace rule, GC formula and nearest-neighbor method for primer melting temperature, and choose a PCR annealing temperature.

• C1V1 = C2V2: how to calculate dilutions

  How to use the C1V1 = C2V2 dilution formula with worked examples for molar solutions, X buffers and primer stocks, plus common mistakes.

• How to count cells with a hemocytometer

  Count cells and check viability with a Neubauer hemocytometer and trypan blue: loading, which squares to count, the formula and a worked example.

• How to resuspend primers and oligos to 100 µM

  How much water or TE to add to a dried oligo for a 100 µM stock, how to make a 10 µM working stock, and how to store primers.

• How to calculate DNA and RNA concentration from A260

  Convert absorbance at 260 nm to DNA or RNA concentration, interpret A260/280 and A260/230 purity ratios, and avoid common measurement errors.

• PCR not working? A troubleshooting checklist for no band

  Why a PCR gives no band and how to fix it: controls, template, primers, reagents, cycling conditions and gel problems, in the order to check them.