Why is serum given as a percentage while supplements use a stock factor?

Serum is a bulk component added by volume, so a 10% final means 10 mL per 100 mL regardless of what is in it. Supplements are concentrated stocks, so you add a tiny fraction such as 1/100 for a 100x item to reach the working dose. Mixing the two units is the usual source of error, so the tool keeps serum on percent and supplements on stock factor.

Can I just add every supplement at 1x directly?

No, adding each supplement as if it were already at 1x working strength would mean adding the full working volume of every component, which would dilute the medium and push the total far past your final volume. You add the small stock volume and let it dilute to 1x in the mix, which is why the calculator subtracts only the stock amount from the basal medium.

How long can I store complete medium after adding serum?

Once serum and heat-labile supplements are in, plan to use the complete medium within about 2 to 4 weeks if stored at 4 C, and not for long-term storage. Serum degrades and some components such as glutamine break down, so many labs prep only what they need for a few weeks. For longer keeping, store basal medium and add supplements fresh.

When do I use 10% FBS versus 2% FBS?

Use 10% FBS for routine growth of most adherent and suspension cells that expect rich feeding. Drop to 2% FBS when weaning cells, holding a maintenance culture, or running a serum-starvation step before a stimulation assay. The lower serum reduces background signaling so treatment effects are clearer.

Media Recipe

Cell Culture Media Recipe Calculator

Work out volumes of serum, supplements and basal medium for any final volume.

Inputs

Final volume (mL)

Serum (FBS)

Supplements

Pen-Strep (100x, 100 U/mL penicillin + 100 ug/mL streptomycin)Stock 100x

L-Glutamine (100x, 200 mM stock to 2 mM working)Stock 100x

Sodium Pyruvate (100x, 100 mM stock to 1 mM working)Stock 100x

NEAA (100x, non-essential amino acids)Stock 100x

HEPES (100x, 1 M stock to 10 mM working)Stock 100x

Beta-Mercaptoethanol (1000x, 55 mM stock to 55 uM working)Stock 1000x

Tip: supplements are added by stock concentration, so each one is only a small fraction of the final volume.

Recipe

Basal medium

440mL

Total additives used: 500 mL

Serum at 10%50 mL

Pen-Strep (100x, 100 U/mL penicillin + 100 ug/mL streptomycin)Stock 100x5 mL

L-Glutamine (100x, 200 mM stock to 2 mM working)Stock 100x5 mL

Add serum and supplements to basal medium and mix; filter-sterilize if the medium is not pre-sterile.

Description

This tool splits a final culture volume into the right amounts of serum, selected supplements and the remaining basal medium. It reads the stock concentration of each supplement so you add a small volume rather than diluting the recipe, and warns when the additives would exceed the final volume.

How to use

Enter the final volume in mL, the serum percentage, and tick the supplements you want to add. The serum volume, each supplement volume and the basal medium left over are shown at once.

Learn more

What it does

The media recipe calculator turns a target flask volume into exact volumes of serum, any supplements you tick, and the basal medium that fills the rest. It is built for routine mammalian culture where you stock several 100x and 1000x additives and want to prep a complete medium without hand-calculating each component. Everything is expressed as a volume in mL against the final volume you set.

How it works

Serum is dosed by volume fraction: V = final volume x serum percent / 100. Each supplement is dosed by its stock concentration, so its volume is V = final volume x target factor / stock concentration, with the default target factor of 1 giving the normal working strength. The basal medium volume is what remains: final volume minus the sum of all added volumes. If that remainder goes negative the recipe cannot be made.

Worked example

For a 500 mL preparation with 10% FBS and Pen-Strep plus L-Glutamine ticked, you add 50 mL of FBS, 5 mL of Pen-Strep (100x) and 5 mL of L-Glutamine (100x), leaving 440 mL of basal medium. If you also tick Beta-Mercaptoethanol (1000x), only 0.5 mL of it is needed.

When to use it

Use this tool whenever you set up a complete medium from basal powder or liquid for a flask, plate or bioreactor. It is the fastest way to scale a recipe up or down while keeping every component at its correct working concentration, and it catches the common mistake of adding too many supplements for a small volume. Pick 10% FBS for routine growth and 2% FBS for weaning or maintenance cultures.

FAQ

Why is serum given as a percentage while supplements use a stock factor?: Serum is a bulk component added by volume, so a 10% final means 10 mL per 100 mL regardless of what is in it. Supplements are concentrated stocks, so you add a tiny fraction such as 1/100 for a 100x item to reach the working dose. Mixing the two units is the usual source of error, so the tool keeps serum on percent and supplements on stock factor.
Can I just add every supplement at 1x directly?: No, adding each supplement as if it were already at 1x working strength would mean adding the full working volume of every component, which would dilute the medium and push the total far past your final volume. You add the small stock volume and let it dilute to 1x in the mix, which is why the calculator subtracts only the stock amount from the basal medium.
How long can I store complete medium after adding serum?: Once serum and heat-labile supplements are in, plan to use the complete medium within about 2 to 4 weeks if stored at 4 C, and not for long-term storage. Serum degrades and some components such as glutamine break down, so many labs prep only what they need for a few weeks. For longer keeping, store basal medium and add supplements fresh.
When do I use 10% FBS versus 2% FBS?: Use 10% FBS for routine growth of most adherent and suspension cells that expect rich feeding. Drop to 2% FBS when weaning cells, holding a maintenance culture, or running a serum-starvation step before a stimulation assay. The lower serum reduces background signaling so treatment effects are clearer.

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