Lab Utilities, Dilutions & Unit Tools

Work out how much stock solution to take for a given final concentration and volume — and, just as important, how much diluent to add to it.

Convert a required force in × g into the rotor speed to dial up on your own centrifuge — the direction you need when transferring a published method.

Convert rotor speed in revolutions per minute to relative centrifugal field in × g, using your own rotor radius — the number a method should actually specify.

Convert catalytic activity between U/L, IU/L, mU/mL, U/mL, µkat/L and nkat/L — and see why the same number from two laboratories need not mean the same thing.

Convert a manual count from an Improved Neubauer chamber into cells per millilitre, allowing for the number of squares counted and the dilution used.

Convert between Celsius, Fahrenheit and kelvin, with the storage and incubation temperatures a laboratory actually runs on and why a few degrees of freezer drift matters.

Convert milliequivalents to millimoles and to milligrams for any ion, using its atomic or molecular weight and its valence — the two numbers the conversion cannot be done without.

Calculate the molar concentration of a solution from the mass weighed out, the formula weight on the bottle and the final volume.

Convert between ppm, ppb, mg/L, µg/mL, µg/L and per cent — and see where the familiar equivalence of ppm with mg/L stops being true.

Work out the percentage strength of a solution as % w/v, % v/v or % w/w — three conventions that share a symbol and mean different things.

Convert mmHg, kPa, cmH2O, atmospheres, bar and psi through the pascal, with the exact definitions and the blood gas unit split that makes the number meaningless on its own.

Find the concentration at the end of a serial dilution series, and see how quickly the total dilution — and the accumulated pipetting error — grows with each step.