Technically, stocks aren't as expensive as they were during the tech bubble, when compared to other commodities
Here's a blast from the past. Remember when gold had 12 straight years of positive returns from 2001 through 2012? Not only that, it outperformed the Dow in ten of those years. When the Dow began making new highs in 2013, it was still down 75% when priced in ounces of gold. Some people made the case that heavy money printing inflated the Dow price, masking the fact that the economy wasn't really in great shape. That take hasn't aged well, with the Dow up another 65% from the 2013 highs. I thought it would be interesting to see where the stock market stands now in terms of gold and some other commodities.
Stocks Priced in Precious Metals
Here is a chart of the Dow along with gold since 1975. Gold lost about half its value from 1980 through 2000, but then surged higher over the next decade. Gold then continued higher as stocks crashed during the financial crisis in 2008-2009. The metal finally topped out in 2011, and then fell nearly 30% in 2013. Now, gold has broken out a bit after chopping around the $1,200-$1,400 range, while the Dow has been hitting new highs.
Below is the chart of the Dow priced in ounces of gold going back to 1910. In mid-2013, as the Dow was making new highs in terms of dollars, the index was trading around its long-term average of about 11 ounces of gold. Stocks have done much better than gold since the end of 2013, with the Dow gaining about 65% compared to gold, which is up about 20% since then. The index is currently right around 20 ounces of gold, close to double the all-time average. It is, however, down 56% from its high of 44 ounces reached at the height of the tech bubble.
If you price the Dow in ounces of silver, then it looks even more expensive. It's about three times the all-time average, yet off about 35% from its all-time high from the tech-bubble years.
Stocks Priced in Other Commodities
If you're not valuing the Dow in dollars, then it seems natural to value them in precious metals like above. Gold and silver have been used as currencies in the past. You can, however, value the Dow in anything. The chart below shows the number of barrels of oil it would take to buy the Dow. Oil collapsed from 2014-2015, sending the Dow higher when priced in oil. It would take about 500 barrels of oil to buy the Dow right now. That's about two and a half times the long-term average of around 200 barrels and 35% off the all-time. Again, stocks are more expensive than normal, but not near their highest level ever, as it is in dollars.
Copper is often referred to as "Dr. Copper" because it is said to have a PhD in economics, and can predict turning points in the global economy. The chart below prices the Dow in pounds of copper. After two big years in 2016 and 2017 (it outpaced stocks in both years gaining 17.5% and 30%, respectively), copper lost 20% in 2018 and has been flat this year. In pounds of copper, the Dow is a bit more than double the all-time average and half its all-time high.
In conclusion, stock indexes are reaching extremely high levels. The Dow is more than double the level it reached at height of the tech-bubble. When pricing the Dow in other commodities, however, it's not as expensive compared to then. In fact, it's lower by anywhere from 35% to 50%.