The Intensity Formula
The intensity formula is Cal Newport's stated law of productivity in Deep Work in 2016, set at page 40: high-quality work produced equals time spent multiplied by intensity of focus. It is presented in the typography of a principle, with capitals and a multiplication sign, and it is not a formula. Nothing in it has a unit, nothing has ever been substituted into it, and no prediction has been derived from it and checked.
What it is
Take the two quantities seriously for a moment. Intensity of focus has no unit, no instrument and no scale. High-quality work produced has no unit either. Nothing has been multiplied by anything. What remains is a sentence about a trade-off, which is a reasonable thing to say, wearing the clothes of arithmetic, which lends it an authority the claim does not have.
This matters more than it might because of what the book argues elsewhere. Newport's own case includes the claim that knowledge work cannot be measured, and the central formula of the book is a measurement claim. Holding both at once is the difficulty the notation conceals.
In effect
Where the formula comes from is part of the assessment. The case Newport builds it on is the publication record of the organisational psychologist Adam Grant, described across pages 38 to 39, and an account of how Grant works that came from correspondence with him in 2013 plus a slide deck he sent. From one professor's self-description Newport derives the formula, and then uses the formula to explain the professor.
He is honest enough to mark the move, writing that his guess is that Grant does not work substantially more hours, and that he argues Grant's approach to batching helps explain the paradox. The equation is still set on the page as a law. At pages 40 to 41 he adds that the idea first occurred to him while interviewing around fifty high-scoring undergraduates for one of his own earlier trade books, which is a self-citation to unpublished interviews.
Attention residue is then imported at pages 41 to 43 to supply a mechanism. Sophie Leroy's work is real and it is about task switching in a laboratory. It is not about academic publication rates, and the gap between the two is not bridged in the text.
What it does not say
It does not state a relationship that could be tested. This is not an unverified finding awaiting a check, it is a claim with nothing in it that could be checked as written, and the distinction is the reason it is filed as not a research claim rather than as unverified.
It does not follow from the attention residue literature. That work supports the narrower claim that switching tasks leaves a cost, which is a different and much more modest statement than a multiplicative law of output.
It does not license being cited as a law or a result. If it is used at all it should be used as a metaphor, and described as one.
Sources
- Newport, C. (2016). Deep Work. Grand Central. The formula at p. 40; Adam Grant's publication record at pp. 38-39; the batching account drawn from correspondence and slides at pp. 39-41; the undergraduate self-citation at pp. 40-41; attention residue imported at pp. 41-43.
- Leroy, S. (2009). "Why is it so hard to do my work? The challenge of attention residue when switching between work tasks." Organizational Behavior and Human Decision Processes, 109(2), 168-181. About task switching in a laboratory, not about publication rates.
- Evidence status set in the vault, 2026-09-13: not-a-research-claim. There is nothing here that could be checked as written. Never cite it as a relationship, a law or a result.