🫙 Media Recipe
| Component | Per Litre | Your Volume | Per Vessel |
|---|
| Batch Volume | Autoclave Time (121°C, 15 psi) | Typical Vessel |
|---|---|---|
| ≤250 mL | 15–20 min | 250 mL flask/bottle |
| 500 mL | 20 min | 500 mL flask/bottle |
| 1 L | 20–25 min | 1 L bottle |
| 1–2 L | 30 min | 2 L flask/bottle |
| 2–4 L | 35–40 min | 4 L carboy |
| 4–10 L | 45 min | 10 L carboy |
| >10 L | Split into multiple runs | Multiple vessels |
| Agar plates (pour temp) | Cool to ~55°C first | Petri dish |
Introduction
The Culture Media Calculator helps microbiologists, molecular biologists, and lab students quickly scale standard bacterial culture media recipes to any preparation volume. Select from 12 common media types — including LB, M9, BHI, SOC, and Terrific Broth — and instantly receive precise component weights, per-vessel amounts, and a complete autoclave protocol tailored to your batch size.
About the Tool
This calculator removes the tedious arithmetic of scaling microbiological culture media recipes. Rather than manually multiplying each component concentration by your target volume, the tool does it instantly and generates a full preparation protocol — saving time and reducing pipetting errors in the lab. It covers 12 standard formulations commonly used in E. coli cloning, expression, and general microbiology work: LB Miller, LB Lennox, LB Agar, M9 Minimal, SOC, BHI, TSB, TSA, Nutrient Broth, Nutrient Agar, 2×YT, and Terrific Broth. Each recipe reflects the standard concentrations referenced in common molecular biology and microbiology protocols.
Understanding the Inputs
Select Media — Choose your desired formulation from the dropdown. Media that are always agar-based (LB Agar, TSA, Nutrient Agar) will automatically include agar in the recipe regardless of the "Include Agar" setting.
Volume to Prepare (mL) — The total batch size you want to make. Enter 1000 for a litre, 500 for half a litre, and so on; the calculator accepts any volume, including non-standard batch sizes.
Number of Flasks / Bottles — If you are distributing your media across multiple vessels (e.g. 4 × 250 mL Erlenmeyer flasks), enter that number here to get a per-vessel breakdown alongside the total recipe.
Include Agar? — Choose liquid broth, solid agar (1.5% w/v) for standard colony plates, or soft agar (0.7% w/v) for overlay and motility assays.
Advanced Options (optional) — Override the default target pH or specify a custom agar percentage if your protocol calls for values other than the standard defaults.
Formula Explanation
The calculator uses a simple linear scaling formula for each component:
Concentration is the standard amount per litre as defined in the media recipe, in grams per litre (g/L) unless otherwise noted. Target Volume is the batch size you enter, in millilitres (mL). For liquid supplements expressed in µL/L (e.g. 1M MgSO₄ stock in M9 minimal), the same scaling factor is applied and the result is returned in µL to preserve accuracy at small scales. Water is always added to final volume rather than by a fixed amount, to account for the volume contributed by dissolved solutes.
Worked Example
Sample Input
Media = LB Agar (Miller), Volume = 1500 mL, Vessels = 3, Agar = Yes (1.5%). Scenario: a grad student needs 1.5 L of LB Agar split across 3 pooled 500 mL bottles, enough to pour roughly 60 plates.
Step-by-Step Calculation
The scale factor is 1500 mL ÷ 1000 = 1.5. Each component's per-litre amount is multiplied by this factor: Tryptone = 10 g/L × 1.5 = 15 g; Yeast Extract = 5 g/L × 1.5 = 7.5 g; NaCl = 10 g/L × 1.5 = 15 g; Agar = 15 g/L × 1.5 = 22.5 g. Dividing the total volume by 3 vessels gives 500 mL per bottle, so each bottle receives exactly one-third of each component amount above.
Final Result
Total recipe for 1500 mL: 15 g Tryptone, 7.5 g Yeast Extract, 15 g NaCl, 22.5 g Agar, topped up to 1500 mL with distilled water. Per 500 mL bottle: 5 g Tryptone, 2.5 g Yeast Extract, 5 g NaCl, 7.5 g Agar. The generated protocol calls for autoclaving at 121°C, 15 psi for 30 minutes (since the batch exceeds 1 L) and cooling to ~55°C before pouring plates.
Interpretation
Because the batch is split across 3 vessels, each bottle can be autoclaved and poured independently without any further calculation — the per-vessel column already accounts for the split. This is especially useful for planning autoclave loads when a single large vessel would not fit or would take longer to heat through.
Interpreting Your Results
The results table lists each ingredient with three columns: the standard per-litre amount, your scaled total amount, and the per-vessel amount. The "Your Volume" column is what you actually weigh or measure. The per-vessel column is useful if you want to prepare batches directly in individual flasks rather than pooling and then distributing. The preparation protocol below the table is specific to the media type selected — media with special requirements (like SOC's glucose addition or Terrific Broth's separate phosphate buffer) include a bolded note at the end of the protocol list. Always read this note before beginning preparation.
Practical Applications
Use this tool whenever you are making a non-standard batch size that does not divide cleanly from a 1 L recipe. Common scenarios include: preparing 200 mL of LB for a small overnight culture, scaling up to 4 litres of Terrific Broth for a large protein expression run, or preparing 48 agar plates from 1.2 L of LB Agar. The vessel-splitting feature is particularly useful for autoclave load planning — you can enter 4 vessels for a 2-litre batch and immediately know you need 500 mL per flask.
The tool is also useful for teaching and training lab personnel. Providing a printed protocol generated from this calculator reduces preparation errors in teaching labs and ensures consistency across batches when multiple operators are involved.
Common Culture Media Uses
- LB (Miller): General-purpose E. coli growth. Most common lab broth for routine cloning, transformation, and overnight cultures.
- LB (Lennox): Low-salt variant preferred for ampicillin selection and electrocompetent cell preparation.
- M9 Minimal: Defined minimal media for metabolic studies, auxotroph complementation, and isotope-labelling (e.g. 15N or 13C NMR studies). Requires a carbon source supplement.
- SOC: High-nutrient recovery media after transformation — improves competent cell recovery efficiency significantly over LB.
- BHI: Rich media for fastidious organisms including Streptococcus, Listeria, and anaerobes that require complex nutrients not present in LB.
- TSB/TSA: General-purpose media for a wide range of bacteria and fungi; used in environmental monitoring and clinical microbiology.
- 2×YT / Terrific Broth: High-density growth media for protein expression cultures and phage propagation. TB supports significantly higher cell densities than LB due to its high yeast extract and buffered phosphate content.
Scientific Notes & Limitations
Recipe concentrations reflect the standard formulations most commonly referenced in molecular biology and microbiology protocols; commercial premixed powders (e.g. BHI, TSB) can vary slightly between manufacturers, so always check the label on your specific product. The calculator assumes standard atmospheric pressure autoclave cycles at 121°C, 15 psi — high-altitude labs or non-standard autoclave equipment may require adjusted times or pressures. pH targets are approximate starting points; always verify with a calibrated pH meter, since pH can drift slightly during and after autoclaving. This tool is intended as a calculation aid for experienced lab personnel and does not replace your institution's standard operating procedures or safety protocols.
Practical Tips
- pH adjustment: Adjust to the target pH (shown in the generated protocol) with 1M NaOH or 1M HCl before autoclaving. Use a calibrated pH meter — indicator strips are not accurate enough.
- Autoclave: 121°C, 15 psi, 20 min for volumes ≤1 L; increase to 30 min for 1–4 L batches. The calculator protocol automatically adjusts autoclave time based on volume.
- Agar plates: Cool to ~55°C before pouring to avoid condensation on lids and thermal degradation of antibiotics. A 55°C water bath is the most reliable way to hold agar at pour temperature.
- Antibiotics: Add after autoclaving and cooling below 60°C. Prepare 1000× stocks in appropriate solvents, filter-sterilise, and aliquot for long-term storage at −20°C.
- Storage: Liquid broth at 4°C up to 3 months; agar plates sealed in plastic sleeves at 4°C up to 4 weeks. Discard if cloudy or contaminated.
Common Mistakes to Avoid
Adding agar before dissolution: Agar does not dissolve at room temperature — it must be autoclaved. However, if components are not fully dissolved before autoclaving, clumping can result in uneven media. Always dissolve salts and nutrient sources in warm water first, then add agar powder and autoclave.
Autoclaving heat-labile supplements: Never autoclave antibiotics, glucose (for M9), or other heat-sensitive additives. These must be prepared as filter-sterilised stocks (0.22 µm membrane) and added to cooled media at approximately 55°C. Autoclaving ampicillin, for example, destroys it completely.
Incorrect pH adjustment: Most bacterial media should be adjusted to pH 7.0–7.4 before autoclaving using 1M NaOH or 1M HCl. pH changes slightly during autoclaving so calibrate at room temperature. Using too much NaOH can lead to caramelisation of sugars during autoclaving if organic components are present.
Pouring agar plates too hot: Pouring solid agar above 60°C causes excessive condensation on lids, which leads to surface moisture that can spread colonies and distort results. Allow media to cool to approximately 55°C (comfortable to hold in a 50°C water bath) before adding supplements and pouring.
Using tap water: Always use distilled, deionised, or MilliQ water to prepare culture media. Tap water contains variable mineral content, chlorine, and microorganisms that interfere with growth and alter media pH and osmolality.