Edit: Being told by @Dr_CMingarelli on twitter that it's 10 meters pr lightyear.
> Gravitational waves are not easily detectable. When they reach the Earth, they have a small amplitude with strain approximately 10^−21
"strain" being the unit-less measurement they use for gravitational wave.
The ones we measured just now, if I'm reading this article right (https://iopscience.iop.org/article/10.3847/2041-8213/acdac6), are being reported as 2.4x10^-15.
I can say that's a lot larger, but I can't tell you much else about what that means.
> Each observatory has two light storage arms that are 4 kilometers in length. [...] A passing gravitational wave will slightly stretch one arm as it shortens the other. [...] Even with such long arms, the strongest gravitational waves will only change the distance between the ends of the arms by at most roughly 10⁻¹⁸ m.
With the nominal hair value being 75 µm, `apt install qalc` tells me that's
> 75 µm / 10^-18 m
(75 * micrometer) / ((10^-18) * meter) = 7.5E13
https://en.wikipedia.org/wiki/Gravitational_wave , https://en.wikipedia.org/wiki/Hair%27s_breadth