With more than 1.5 million votes still left to count, turnout for California’s March 3 primary looks like it will be good, but not approaching record territory.

“When everything is counted, it looks like the percentage of registered voters will be about 47, 48 or 49%,” said Paul Mitchell of Political Data Inc., which tracks voting information for campaigns and other political groups. “That’s about the same as in 2016.”

That would be well below the 57.7% turnout in 2008, when Barack Obama and Hillary Clinton squared off in the Democratic primary. And that total fell short of figures in the 1976 primary (72%) and 1980 (63%).

The number of late votes can mean delays in determining the winners and losers. For example, it wasn’t until Wednesday, more than a week after the election, that the Proposition 13 school bond measure was declared a loser, with 54% of the voters opposed.

Although the turnout percentage won’t be in record territory, the sheer number of voters is still impressive.

There were a record 20.7 million registered voters in the state this year, up from 17.9 million in the June 2016 presidential primary. That registration boost, along with the growth in California’s population, means that far more ballots were cast this year than four years ago.

There were 8.5 million voters in 2016, but this year’s count was already 8.1 million as of Wednesday morning, with uncounted ballots likely to push that number closer to 10 million.

Who those new voters were is impossible to tell just yet, Mitchell said.

“We’ll know a lot better in six to eight weeks, when the counties release their final totals,” he said. “But not all those new voters are the result of increased registration. A good amount came from voters already on the rolls, but who hadn’t voted in the past.”

Political enthusiasm is a major factor in California. A February poll by the Public Policy Institute of California found that 63% of the state’s adults were unhappy with the job President Trump was doing and 58% wanted him impeached and removed from office. Democratic leaders were confident that those strong feelings would bring out anti-Trump voters.

An exit poll conducted by Edison Research found that 10% of California voters interviewed on Super Tuesday had never before cast a ballot in a Democratic primary.

The 38% turnout for the June 2018 election also stoked hopes for a surge of voters this year, since that was the strongest showing by voters in a nonpresidential primary since 1998.

Although the early vote returns were disappointing to Democrats, particularly in a number of tough congressional races, votes counted since election night have swung the Democrats’ way. Party leaders are confident that the inevitable higher turnout for the November election will provide the partisan increase they had hoped for in the primary.

“In 2018, many Republicans running for the House prematurely declared victory, only to find themselves at home when Congress started,” said Andy Orellana, a spokesman for the Democratic Congressional Campaign Committee. “Now ... they’re willing to make the same mistakes by spending millions crowing about primary votes that are still being tabulated.”

Republicans, although heavily outnumbered in the state, believe their showing on March 3 proves they can take back at least some of the seven House seats the Democrats took from the GOP in 2018.

“You would think Democrats already had a greater incentive than Republicans to show up in March, given the contested presidential primary,” said Torunn Sinclair, a spokeswoman for the National Republican Congressional Committee. “But, hey, whatever the Democrats have to tell themselves to sleep at night.”

There’s no doubt the numbers will swell in the November election, as occasional voters and those without a party preference historically have shown up for the presidential contest. Since 2000, the turnout for each of those elections has been 70% or better.

One thing Republicans will have to deal with has been the tendency of the late-arriving ballots to skew heavily Democratic. In 2018, Republicans led in four of the seven targeted House seats on election night. When those late ballots were counted, the GOP had lost every one.

“There’s a real leftward tilt to those late voters,” Mitchell said, noting that early voters tend to be older and more conservative.

“You don’t have 65-year-old homeowners in the hills of Orange County doing same-day registration,” he said. “You do have that for 25-year-olds who may be sleeping on their sister’s couch.”

One record that is likely to be broken this election is the number of uncounted ballots left after election day. Although the first report from the state on the day after the election suggested that slightly more than 3.1 million ballots remained to be tallied, the actual number was probably much higher.

“Those first numbers provided by counties are often estimates,” sometimes provided by weighing bags of ballots rather than actually counting them, Mitchell said. “It also didn’t include all the ballots that arrived after the election but were postmarked by election day.”

That final number can’t be determined until the final results are released next month, but it may turn out that as many as 4.5 million ballots were counted after the election, which would be better than 45% of all that were cast.

John Wildermuth is a San Francisco Chronicle staff writer. Email: jwildermuth@sfchronicle.com Twitter: @jfwildermuth