The formulas
volume per reaction = final ÷ stock × reaction volume
mix = per reaction × reactions × (1 + extra %)
Water makes up the reaction volume after the components and template. Template is added to each tube separately, so it is not in the mix.
Worked example
A 25 µL PCR with 2X master mix (12.5 µL), primers from 10 µM to 0.5 µM (1.25 µL each), 2 µL template and 8 µL water. For 12 reactions plus 10% extra, make enough for 13.2: 303.6 µL of mix, then add 23 µL to each tube.
Common questions
Should controls count as reactions?
Yes. Count no-template and other controls in the number of reactions.
Percentage or extra reactions?
Both are common. 10% extra suits most plates; one or two extra reactions suits small runs.
This calculator is checked against independent calculations before every release. How we check our calculators.