Acceleration is the rate of change of velocity.
Gravity gives an acceleration of 32 ft/sec/sec
An aircraft doing 150kt (no wind) on a 3 degree glideslope has a vertical velocity of 13.3 ft/second.
The formula we need is
v squared = u squared + 2as
where u is initial velocity
v is final velocity
a is acceleration
s is distance travelled between u and v
We have u=13.3, v=0
All the vertical deceleration occurs in compression of the oleos and tyres. Say a movement of 3 feet. Assume the load/deflection curve is uniform over that 3 feet, and oleos do not hit limits.
Then a = u squared / 2s = 13.3* 13.3 / (2 * 3) = 29.5 = 29.5/32g = .92 extra gs
Note the effect of the v squared
If you can at the last moment halve the vertical speed to say 6.6 ft/sec while the oleos are deflecting, you get only 0.23 extra g.