Agar & Media Calculator
Pick your recipe — LMEA, MEA, or PDA — enter how many plates or slants you're pouring and at what volume, and get the exact grams of agar, malt extract or dextrose, potato or peptone, and water to weigh out. Scaled to any batch size by a grower and fermentation scientist.
30–45 min at 15 psi (250°F); pour at ~120–130°F.
Scale any agar recipe to your exact plate or slant count.
Every recipe here is written per litre of finished media, then scaled by your total volume. Pour too little and you're back in the kitchen mid-transfer session; pour too much and you've wasted malt extract and agar that won't be used before it dries out in storage. This tool takes the recipe you're already running, multiplies it out for the batch size in front of you, and hands back grams — not guesses.
Everything runs client-side. Nothing is stored, nothing is sent — change any input and the result updates live.
The recipes, explainedFour media, one scaling method.
Total volume = count × volume each
Everything starts with how much finished media you actually need. Multiply your plate or slant count by the volume you pour into each one, and every ingredient below scales off that one number as a fraction of a litre.
total_volume_mL = count × volume_each_mL
scale = total_volume_mL ÷ 1000 # fraction of a litre
ingredient_g = recipe_g_per_L × scale
LMEA — light malt extract agar
The standard general-purpose culture medium for gourmet mushroom work: clear enough to see contamination early, forgiving enough for most species. Per litre: light malt extract 20 g + agar 20 g.
MEA — malt extract agar
A slightly richer relative of LMEA, sometimes with peptone added for extra nitrogen on fussier or slower species. Per litre: malt extract 20 g + agar 20 g, with peptone 2 g as an optional addition.
PDA — potato dextrose agar (DIY)
Made from a real potato infusion rather than a powder — a step closer to what a mushroom finds in the ground, and a favorite for reviving sluggish or wild-collected cultures. Per litre: potato 200 g (infusion) + dextrose 20 g + agar 18 g.
PDA — commercial powder
Pre-blended potato dextrose agar powder, weighed and dissolved directly — no potato boiling, no straining. Per litre: 39 g of powder.
40 plates × 20 mL = 800 mL of LMEA. Scale = 800 ÷ 1000 = 0.8.
Light malt extract: 20 g × 0.8 = 16 g. Agar: 20 g × 0.8 = 16 g. Water: to ~800 mL total.
Dissolve, sterilize, and pour — that's ~40 plates. Make a little extra for bubbles and spills.
When the standard number is wrong.
These recipes are solid, source-verified starting points — not the only correct answer. Here's where blindly trusting a preset costs you a batch.
Agar % sets firmness — and 2% is the standard set
Agar concentration is what makes the plate a solid instead of a soup. ~2% (20 g per litre) is the standard set across LMEA and MEA for a reason: much less and the media won't gel firm enough to streak or pour clean plates; much more just wastes agar without buying you anything — plates that are needlessly stiff and harder to work with. Stay close to 2% unless you have a specific reason to move off it.
Volume per plate is a real choice, not a fixed number
The 18–25 mL range isn't padding — it's a real trade-off you're making every time you pour. A thin pour (18 mL) stretches your media further and gives you more plates per batch, but those plates dry out faster in storage and give you less working depth for isolation work. A thicker pour (25 mL) stores longer and gives more room to cut and transfer, but costs more media per plate and yields fewer plates from the same batch. Pick a volume and be consistent — that's what makes your plate counts (and your ordering) predictable.
MEA and PDA aren't single recipes
Don't treat the numbers on this page as the only version of these media that exists. The literature has real variation: malt-to-agar ratios show up as both 20:20 and 30:15 depending on the source, and DIY potato dextrose recipes call for anywhere from 200 g to 300 g of potato per litre. The presets here are solid, workable starting points — if you're chasing a specific texture or growth rate and these aren't giving it to you, that's a sign to adjust the ratio deliberately, not that you've done something wrong.
Antibiotics are deliberately left out
You won't find a gentamicin or antibiotic dose on this page, and that's on purpose. Hobby-scale doses reported in the wild span an enormous range — 10 to 500 mg per litre — and even at the high end they only knock back some bacteria, not all of it, while doing nothing for mold contamination. Antibiotics can mask a bad habit instead of fixing it. If your plates keep contaminating, the higher-leverage fix is almost always clean flow-hood technique — proper still-air zone, minimal movement across the pour, sterile tools — before you reach for a dosing chart.
Notes from the farmAgar work is where fermentation-lab habits transfer straight over to mushroom farming — it's the same instinct to respect the sterile boundary whether you're streaking a yeast plate or a mycelium plate. The number that trips people up most isn't a ratio, it's pour temperature. Pour too hot and you cook condensation into the lid, which becomes free water for contaminants to swim in later; pour too cool and the agar starts setting in the pot before you've filled your last plate. ~120–130°F is the window — warm enough to stay liquid and pour clean, cool enough that the glass doesn't scorch your hand through a glove. Get that one number right and the rest of the recipe takes care of itself.
Track every batch, flush, and yield — not just the pour.
A media batch is one step in a much longer chain. The value shows up when you log it against every batch, flush, and yield across your grow rooms — and see which room is drifting toward a contamination problem before you lose a crop. That's what a Farm-Ops tracker does automatically.