Stock Solution Calculator

How to make a 1000× stock solution

1. Choose an antibiotic or Other, and check the working concentration.
2. Set the stock strength, usually 1000×.
3. Enter how much stock to make and the volume of media or agar; the mass to dissolve and the volume of stock to add appear.

Frequently asked questions

What does 1000× mean?

The stock is 1000 times as concentrated as the working solution, so you add 1 µL per mL of media. Ampicillin at 100 µg/mL becomes a 100 mg/mL stock, and 500 mL of agar takes 500 µL.

Which solvent do I use?

Water for ampicillin, carbenicillin, kanamycin and spectinomycin; ethanol for chloramphenicol and tetracycline. Filter-sterilize water-based stocks rather than autoclaving them.

When do I add antibiotics to agar?

After autoclaving, once the agar has cooled to about 50 to 55 °C, so the antibiotic is not damaged by heat.

Are the working concentrations fixed?

They are common values. Plasmids, strains and protocols vary, so follow your own protocol when it differs.