GIFSQ Tools · Module 3 — Food Microbiology & Enumeration · Tool 054 of 500
Work out how much dehydrated medium powder to weigh for a batch, and how many plates it will fill.
Try sample values — fills the form with the worked example below.
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Powder needed (g)
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Volume (mL)
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Plates filled
Equation: Powder (g) = concentration (g/L) × volume (L); plates = total volume (mL) ÷ volume per plate (mL).
Method: Dehydrated media preparation per ISO 11133:2014 (preparation, production, storage and performance testing of culture media) and the manufacturer's label directions.
Assumptions: The powder is fully dissolved in the stated volume of water and the label concentration is for the finished medium.
Limitations: Supplements, blood or other additions are not included — add them after autoclaving per the label. Weighing error grows when the batch is very small; prepare at least 100 mL where possible.
Rounding: Powder to 2 decimal places; plates to 1 decimal place; intermediates unrounded.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Method: Dehydrated media preparation per ISO 11133:2014 (preparation, production, storage and performance testing of culture media) and the manufacturer's label directions.
Assumptions: The powder is fully dissolved in the stated volume of water and the label concentration is for the finished medium.
Limitations: Supplements, blood or other additions are not included — add them after autoclaving per the label. Weighing error grows when the batch is very small; prepare at least 100 mL where possible.
Rounding: Powder to 2 decimal places; plates to 1 decimal place; intermediates unrounded.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Worked example: Plate Count Agar at 28 g/L, 1,000 mL to prepare, 20 mL per plate: powder = 28 × 1 = 28.00 g; plates = 1,000 ÷ 20 = 50.0 plates.
Enter values above to see results.
Always check the label concentration — it differs between media and suppliers. Tool 054 of 500 — GIFSQ
