Gold Price
The gold price is around $4000 per troy ounce (toz). In 1971 the gold price was around $40 per troy ounce. It might make more sense to measure something that has dramatically increased in volume ($) against something with a relatively static volume (gold). The dollar price was 0.025 toz in 1971 (1/40) and is currently around 0.00025 toz (1/4000).
So the dollar has lost 99% of its purchasing power relative to gold since 1971 (0.025-0.00025)/0.025*100).
A common analogy is that one troy ounce of gold was enough to buy a toga in Roman times and is still enough to buy a suit today.
“Paper money eventually returns to its intrinsic value – zero.” Voltaire, 1694-1778
Paper Gold price versus Physical Gold price
The gold price is set in the paper market (including futures derivatives) which is about 100 times as big as the physical gold market according to some estimations. There is a theory that the gold price has been manipulated down in this market. If buyers prioritise physical gold over paper gold then pricing power could move from the paper market to the physical market. This would limit the opportunity to manipulate the price.
Physical Gold Demand
Central banks have been big buyers of physical gold recently. Investment banks are forecasting an increased gold price as the global money supply continues to expand.