The formula
C₁ × V₁ = C₂ × V₂ → V₁ = C₂ × V₂ ÷ C₁
C₁ is the stock concentration, V₁ the volume of stock to add, C₂ the final concentration and V₂ the final volume. Make up to V₂ with diluent, so diluent = V₂ − V₁.
Worked example
To make 100 mL of 50 mM Tris from a 1 M stock: V₁ = 0.05 M × 100 mL ÷ 1 M = 5 mL of stock plus 95 mL of water. That is a 1:20 dilution.
Common questions
Can I mix units, like M and mg/mL?
Units within one family convert automatically (mg/mL to µg/mL, M to nM, and % w/v to mg/mL). Molar and mass units need a molecular weight, so use the concentration converter first.
What if the stock volume is tiny?
Set your smallest reliable pipetting volume. If the answer falls below it, the calculator plans one or more intermediate dilutions so no step goes under that limit.
Does it work for 10X buffers?
Yes. Choose X for both concentrations: 10X to 1X in 500 mL needs 50 mL of stock.
This calculator is checked against independent calculations before every release. How we check our calculators.