The 40/30/1 Rule
40 words max. 30 point minimum font. 1 slide per minute. Anthony Greiter's 40/30/1 Rule is not a preference, it is a non-negotiable standard built on how human brains actually process information on stage.
Research confirms it. When slides are packed with text, audiences stop listening and start reading. The 40 word maximum in the 40/30/1 Rule exists because of this exact cognitive reality. You cannot serve both at once.
Cognitive load theory explains why dense slides kill comprehension. Cleaner, simpler slides reduce the mental effort required to process information, leaving more room for the audience to actually absorb what the speaker is saying.
A 30 point minimum font is not a design preference. It is a communication standard. If any member of the audience has to strain to read a slide, the slide has already failed before the speaker opens their mouth.
Guy Kawasaki's 10-20-30 Rule is the closest thing in the mainstream to Anthony's 40/30/1 standard. Both frameworks exist for the same reason: unlimited slides produce unlimited forgettable presentations. Constraints force clarity.
The 40/30/1 Rule is grounded in cognitive load theory, the science of how much information a brain can process at once. Understanding this is what separates slides that help audiences think from slides that overwhelm them.
The most common pushback from scientists is that they have too much data to follow the 40/30/1 Rule. That is exactly backwards. The more complex the data, the more the audience needs simplicity around it to understand it.
The 40/30/1 Rule treats slide design as a communication decision, not an aesthetic one. Every element on a slide either helps the audience understand or gets in the way. There is no neutral.