The number one reason I would buy Rio Tinto shares

Rio Tinto Ltd (ASX: RIO) shares are popular with mining investors.

It isn't hard to see why. From its enormous iron ore operations to its expanding lithium business, there's plenty to like.

But they are not the number one reason I would buy its shares today.

What is the number one reason I'd buy Rio Tinto shares?

The reason I am most positive on Rio Tinto is its exposure to copper.

I believe the miner is building a much stronger position in a metal that could become increasingly valuable over the next decade.

And unlike some miners hoping to develop copper projects in the future, Rio Tinto is already delivering meaningful production growth.

Why I think copper has a bright future

One of the biggest reasons I'm bullish on copper is the enormous amount of investment needed in electricity infrastructure.

Whether electricity comes from a power station, solar panels, or a wind farm, it still needs to reach homes and businesses.

That requires copper for cables, transformers, and electricity networks. And as electric vehicles become more common and AI data centres consume increasing amounts of electricity, I believe the world will need considerably more copper.

The challenge is producing enough of it. New copper mines can take many years to develop, and companies are increasingly facing difficulties finding attractive deposits, securing approvals, and managing development costs.

The International Energy Agency's latest outlook suggests that announced mining projects could leave global copper supply approximately 25% short of requirements by 2035.

I think that creates an interesting opportunity for established producers with major projects already underway.

Rio Tinto's copper ambitions

The company's Oyu Tolgoi mine in Mongolia is becoming one of the world's largest copper operations.

The underground mine is ramping up, with copper production increasing 29% during the first nine months of 2026.

And there's more growth ahead. Rio Tinto expects Oyu Tolgoi to produce approximately 500,000 tonnes of copper annually, on average, between 2028 and 2036.

That's across the combined open-pit and underground operations, in which Rio Tinto holds a 66% interest.

I think having that level of production for almost a decade could prove enormously valuable if copper demand continues growing.

But Oyu Tolgoi is only part of the story. Rio Tinto is targeting an increase in its total copper production from approximately 880,000 tonnes in 2025 to 1 million tonnes annually by 2030.

It's also pursuing production growth at its Kennecott operations in the United States, alongside longer-term opportunities such as the Winu copper-gold project in Western Australia.

And just last week, Rio Tinto approved another US$144 million of investment at the Resolution Copper project in Arizona.

The project is still in development, but it has the potential to become one of America's largest copper mines.

I believe this combination of existing production growth and future projects could position Rio Tinto exceptionally well over the coming decades.

Would I buy Rio Tinto shares at current prices?

I think the current valuation provides another reason to consider buying.

According to CommSec consensus forecasts, Rio Tinto is expected to generate earnings per share of $11.93 in FY26 and $12.12 in FY27.

At $153.50, that puts the shares on forward price-to-earnings (PE) ratios of approximately 12.9x and 12.7x, respectively.

I think that's a reasonable valuation for a major mining company with Rio Tinto's assets and growth opportunities.

And don't forget the income. Consensus estimates are for fully franked dividends of $6.56 and $6.66 per share in FY27 and FY28, which imply dividend yields of around 4.3%.

Foolish takeaway

For me, copper is the biggest reason I'd want to own Rio Tinto shares.

The company has already invested heavily in building its production capacity, and I believe those investments could become increasingly valuable as global copper demand grows.

With the shares trading on a reasonable earnings multiple, I'd be happy to buy today and give Rio Tinto's copper ambitions time to deliver.