Wikipedia used to say atoms typically vibrate about ten pico meters (1 x 10^-11 meters). Iron atoms are around 300 picometers across, which means vibration is in the range of 3.3% of its size.

There is no longer anything on the internet which says what the amplitude of atomic vibrations is. Complex formulas are given for taking into account a large number of details.

Here's the quote that used to be on Wikipedia at this address: https://en.m.wikipedia.org/wiki/Atom_vibrations

"The atoms and ions of a crystalline lattice, which are bonded with each other with considerable interatomic forces, are not motionless. Due to the consistent vibration induced through thermal energy, they are permanently deviating from their equilibrium position. Elastic waves of different lengths, frequencies, and amplitudes run through crystalline solids at all times. The typical order of the atomic vibrations frequencies is -011¹³ Hz (later = 10¹³), and that of the amplitudes is 10^-11 m."

The amplitude of 10^-11 meters is ten picometers of atomic vibrations. The ligo experiment says motion was measured down to 0.1 attometers (1 x 10^-19 meters). The ratio is determined by subtracting exponents, which is 10⁸. That's 100 million. In other words, 10^-19 times 10⁸ equals 10^-11.

Here is the quote from the web site for gravity wave measurements, called LIGO:

"The change in distance between LIGO's mirrors (test masses) when a gravitational wave passes will be on the order of 10^-19 m. To achieve this level of sensitivity, LIGO..."