If you compare it with Gold - against which the USD moved in lockstep until the US left the Gold Standart - it's a lot worse than just a 50% loss since 2013, more like a 65% of value.
The fall is probably the same in terms of real inflation (as actually felt by people in terms of how much less their money buys) - the official inflation figures understate inflation (probably because the mathematical calculation for GDP involves raw GDP being deflated by inflation, so the less the official inflation is the more politicians can harp about how much they made GDP "grow") and this has been going on for decades, which is why a single blue collar salary that used to be enough for a good house, a car and the expenses for a family of 5 in the 60s, now can barelly pay the rent of small appartment in a major city.