Facebook founder Mark Zuckerberg sat in a big-boy seat on Tuesday — as he used a height-boosting cushion during his grilling before the Senate.

The 5-foot-7 executive squirmed in a chair that included a 4-inch-thick pad under his behind while being blasted for hours with questions from lawmakers about his social network’s handling of user data.

“Mark Zuckerberg’s chair on Capitol Hill has a nice big extra cushion,” tweeted The Washingtonian, which first noticed the seat booster.

A rep from Facebook said the cushion was not the billionaire’s private seat, but was provided by the Senate Judiciary Committee.

“That’s the committee’s standard practice,” a company spokesperson told The Post.