This tool estimates number of yeast cells needed to properly ferment specific beer (based on beer style, it's volume and gravity), estimates number of available yeast cells (based on yeast type and age) and finally helps to determine volume and gravity of appropriate (up to 5 steps) starter.
The tool uses information from Yeast: The Practical Guide to Beer Fermentation book, fromBraukaiser blog and from Pivařka book.

Finished Starter yeast cell count N is calculated from following equation N = (I + G) * V * S where I represents Initial Cells in billions per gram of extract, G represents Growth Rate in billions per gram of extract, V represents Starter Volume in Litters and S represents DME Mass Concentration.
Growth Rate depends on starter aeration type and I (Intial Cells Per Extract (B/g)).

• Stirred starters: if I < 1.4 then G = 1.4. If I is between 1.4 and 3.5 then G = 2.33 - (0.67 * I). If I > 3.5 then G = 0.
• Manually shaken starters: if I < 3.5 than G = 0.62. If I > 3.5 than G = 0.
• No agitation: if I < 3.5 than G = 0.4. If I > 3.5 than G = 0.

This tool can be also optionally used to calculate overbuild starter (when brewer harvests yeast for future brews directly from starter) including pitch and harvest volumes (starter must be well-stirred before splitting).

Notes:

• Tool is available for registered users only.
• Choose units.
• Enter Batch Size (wort volume in fermenter) and Original Gravity.
• Enter Coefficient according to following instructions:
  • 0.75 - ALE (up to 15°Plato)
  • 1.0 - strong ALE (more than 15°Plato)
  • 1.5 - lager
  • 2.0 - strong lager
• Optionally enter Overbuild cell count.
• Choose number of starter steps (up to 5).
• Choose yeast type - dry, liquid or slurry - and enter manufactured/harvested date, usage date (date of starter preparation) and available yeast amount (enter number of packs or vials when using Liquid yeast). Alternatively, the amount of available cells can be entered directly.
  • Note: Cells Available field must contain some value otherwise the next steps won't work...
• For each starter step specify it's Aeration type (Stir plate, Manually shaken, No agitation), volume and gravity (recommended value is 9° Plato or 1.036 SG).
• Tool calculates DME weight needed to achieve required starter volume&gravity.
• Besides Final Cell Count, this tool provides a couple of additional information:
  • Cells Per Extract (Billions per gram of extract).
  • Inoculation Rate (milions/mL). To achieve "best results" keep it between 25 and 100.
  • Growth Rate (G).
  • Growth Factor. Should be at least 1.0 for "best" results.
• Tool calculates Pitch&Harvest volumes if Final Cell Count is high enough (and Overbuild Cells count was specified).