Concentration

mg/mL = mass (mg) ÷ volume (mL)

Example peptide A: 10 ÷ 2.00 = 5.00 mg/mL. One mg/mL is one µg/µL, so the same solution is 5.00 µg/µL and 5,000 µg/mL.

Aliquot volume

volume (µL) = mass (µg) ÷ concentration (mg/mL)

A 250 µg portion of the 5.00 mg/mL solution occupies 50 µL. The portion is a laboratory amount of the solution. It is not a quantity assigned to a person or an animal.

Molarity

mM = (mass in grams ÷ molecular weight in g/mol) ÷ liters × 1,000

Example peptide A is 0.010 g in 0.002 L. Dividing by 1,203.4 g/mol and converting to millimolar gives a result just over 4.15 mM. Use the molarity calculator when you want the unrounded figure. Molecular weight has to come from the supplier or a reference database. This site does not invent one for a real compound.

Dilution

C1 × V1 = C2 × V2

Final volume is stock concentration times stock volume, divided by the target concentration. Diluent volume is final volume minus stock volume. If the target is higher than the stock, the calculator stops. It does not tell you to concentrate a solution.

A serial dilution repeats that idea. A factor of 10 means each step is one tenth of the previous concentration. If each tube holds a fixed volume, transfer volume is that volume divided by the factor, and the rest of the tube is diluent.

Mass still in the container

mass (mg) = concentration (mg/mL) × volume remaining (mL)

At 5.00 mg/mL, 1.50 mL still in the vial is 7.50 mg of solid-equivalent mass.

Units

1 g = 1,000 mg = 1,000,000 µg
1 L = 1,000 mL = 1,000,000 µL
1 mg/mL = 1 µg/µL = 1,000 µg/mL = 1,000 mg/L
1 M = 1,000 mM = 1,000,000 µM

Microgram is sometimes written mcg. This site uses µg in the calculators and treats mcg as the same unit when you are reading a label.