Why You Should Report IC₅₀ in micromolar (and How to Convert Quickly)

 How to Convert IC₅₀ Values from µg/mL to µM

When you’re reading pharmacology or microbiology papers, you’ll often see IC₅₀ (half-maximal inhibitory concentration) values reported in µg/mL rather than the more familiar molar units such as µM or nM.

That’s fine when you only care about mass per volume, but if you want to compare different compounds on an equal footing, you need to express their IC₅₀s in molar concentration. Molar units take into account each compound’s molecular weight (MW), so you’re comparing actual numbers of molecules rather than grams.

This post walks you through how to convert any IC₅₀ reported in µg/mL into µM.

Step 1: Understand the Units

• µg/mL means micrograms of compound per milliliter of solution.
  
  

• 1 µg/mL = 1 mg/L = 0.001 g/L.
  
  

To get to moles per liter, we need two conversions:

1. Mass to grams
   
   

2. Grams to moles using the compound’s MW.
   
   

Finally, we convert moles to micromoles (µM).

Step 2: The Conversion Formula

If:

then:

This gives the concentration in µM.

Step 4: Quick Reference Table

IC₅₀ (µg/mL)	MW = 100 g/mol (µM)	MW = 250 g/mol (µM)	MW = 500 g/mol (µM)
1	10.0	4.0	2.0
5	50.0	20.0	10.0
10	100.0	40.0	20.0

(Use the formula for any other numbers.)

Why This Matters

Reporting IC₅₀ values in µM allows you to:

• Compare different compounds fairly, regardless of molecular weight.
  
  

• Better interpret dose–response curves.
  
  

Communicate results clearly to chemists and pharmacologists.