Legiters don’t know exactly how much of a boost “Young Frankenstein” gave the Broadway cume last week — but it was a big one.

Although “Frankenstein” producers Mel Brooks and Robert F.X. Sillerman have decided not to report sales figures for their big-budget new tuner, a combination of digging and number-crunching yielded an estimated box office tally of about $875,000.

That’s net gross for an abbreviated week of four previews. The monster sum lands “Frankenstein” in the No. 6 spot in the top 10, and pushes the show’s average ticket price up to about $205. (A cluster of “Frank” seats carry a premier pricetag of $450, while another chunk sell for $375.)

“Frankenstein” makes the tally for the other new entry of the week — the Kevin Kline-Jennifer Garner starrer “Cyrano de Bergerac” ($344,031 for three previews) — look like small change, even though that production’s inaugural outing broke the first-night record at the Richard Rodgers Theater.

“Cyrano” and those estimated sales of “Frankenstein” helped drive total Rialto grosses up about $1 million to a bit more than $17 million, although it was a mixed week in general for the 27 shows on the boards.

Gaining the most steam last week was “The Drowsy Chaperone” ($628,505), up by more than $110,000, while “The Phantom of the Opera” ($739,663), saw a nice $90,000 bump in biz.

On the other side of the scales, “Curtains” ($550,017) fell by $240,000 in the absence of star David Hyde Pierce, who had the week off. “Rent” ($268,082) was down $185,000 now that original stars Anthony Rapp and Adam Pascal have finished their stint in the show, while “The Color Purple” ($748,722) slid about $120,000.

Otherwise, the ups and downs of individual shows were generally not dramatic. Among the newer play offerings, “Mauritius” ($247,991) stepped up more than $50,000, while previewing “A Bronx Tale” ($195,913) played six previews — two more than the prior sesh — and also rose about $50,000.

Overall, box office hasn’t seemed terribly destabilized by press coverage of a potential work stoppage due to the labor dispute between producers and stagehands. The League of American Theaters and Producers issued a statement Monday assuring ticket buyers the shows would go on throughout this week.