# Fermi numbers
> About 40 seconds after the explosion the air blast reached me.
> I tried to estimate its strength by dropping from about six feet small pieces of paper before, during, and after the passage of the blast wave.
> Since, at the time, there was no wind I could observe very distinctly and actually measure the displacement of the pieces of paper that were in the process of falling while the blast was passing.
> The shift was about 2 1/2 meters, which, at the time, I estimated to correspond to the blast that would be produced by 10,000 tons of TNT.
>
> — _Enrico Fermi, [Top Secret interview](http://www.dannen.com/decision/fermi.html?utm_source=longform.asmartbear.com&utm_campaign=longform.asmartbear.com&utm_medium=post) July 16, 1945, declassified in 1965_, output blast was 21K tons of TNT
- No ranges
- only powers of 10: 0.1, 1, 10, ... 100000, 1M...
## Reference
- [Fermi ROI: Fixing the ROI rubric](https://longform.asmartbear.com/roi-rubric/)
## Avoid wishy-washy estimation words
- \[un\]likely
- probably
- few
- many
- almost always/never
[source](https://longform.asmartbear.com/probability-words/)
| Probability Word | Probability Value | Expected Range |
| -------------------- | ----------------- | -------------- |
| Certain | 100% | 100% |
| Almost Certain | 93% | 87% … 99% |
| Probable | 75% | 63% … 87% |
| Chances About Even | 50% | 40% … 60% |
| Probably Not | 30% | 20% … 40% |
| Almost Certainly Not | 7% | 2% … 12% |
| Impossible | 0% | 0% |