We estimate that over 90% of farmed animals globally are living in factory farms at present. This includes an estimated 74% of farmed land animals (vertebrates only) and virtually all farmed fish. However, there is substantial uncertainty in these figures given the land animal estimates’ heavy reliance on information from Worldwatch Institute with unclear methodology and limited data on fish farming.
In total, we estimate that around 31.0 billion land animals and 38.8 to 215.9 billion fish are being farmed globally at any given time.
We estimate that fish comprise around 78% of farmed animals globally, chickens raised for meat 12%, and chickens raised for eggs 5%, while cows and pigs each comprise only 1%. Our lower and upper bounds are 56-87% for fish, 7-24% for meat chickens, 3-10% for egg-laying hens, 1-2% for cows, and 0-1% for pigs.
 This is based on our knowledge of their confinement and living conditions, though there is limited data on fish farm conditions and no standardized definition. Our total estimates of US farmed fish are based on fishcount.org.uk annual slaughter estimates and Animal Charity Evaluators lifespan estimates (see sheet “Fish Estimates” in the embedded spreadsheet).
Please note that a CAFO as defined by the EPA and what the public would regard as a "factory farm" are not necessarily the same. For instance, a farm with 37,500 chickens or 3,000 pigs is only considered a CAFO if it meets certain conditions regarding surface water pollution, but farms of these sizes that don't meet these conditions could still house animals in ways that would be publicly regarded as crowded "factory" conditions.