Knicks rookie RJ Barrett looked down at his muscular arms after being asked about the different level of physicality found in the NBA following the Knicks’ first practice.

“We got the vets here — big, strong guys, definitely a different level of physicality,’’ Barrett said Tuesday. “I’m going to get used to it. I’ve got a good body.’’

As much has been made about his offensive game that saw rough patches at July’s summer league, the 6-foot-7 former Duke sniper said he knows defense will earn him his rookie minutes, the way coach David Fizdale is preaching.

“Really right now I’m working my tail off on the defensive end,’’ Barrett said. “I’m just trying to get better there. Coach always wants a defensive guy on the court, you know? So if I could do that starting out. … It’s funny. If you’re smart on how you do things and keep your movements precise, that will even give you an advantage or help you keep up with a stronger guy.’’

During voluntary scrimmages in September, Barrett said he played once with ex-Knick Carmelo Anthony, who is unemployed. Anthony was on his team.

“He came and scrimmaged with us once,’’ Barrett said. “He was on my team though. He was good. I mean, it’s Carmelo Anthony. C’mon.”

Barrett’s 3-point shooting was below average at Duke (30.8 percent). At summer league he shot 23 percent. He worked on his stepback 3 during the end of practice Tuesday and admitted the deeper NBA 3-point line is a challenge.

“It’s an adjustment,’’ Barrett said. “I’ve been working on it since I declared for the draft. Like anybody, it’s an adjustment but I’ll be fine, I’ll figure it out.’’

During an online chat with fans last month, he was asked whom he’d like to dunk on the most. Barrett said ex-Knick Kristaps Porzingis. He wouldn’t stoke the flame Tuesday.

“To be honest, I think it’s about anybody,’’ the 19-year-old southpaw said. “Anytime I get the opportunity – who wouldn’t. Everyone wants to dunk on everybody.’’

Fizdale said their other rookie, second-rounder Ignas Brazdeikas of Michigan, had his “welcome moment’’ to the NBA.

Dennis Smith Jr. threw a lob for Kenny Wooten, who flushed it down over Brazdeikas. Wooten is on an Exhibit 10 G-League contract but is hopeful of that turning into a two-way deal.

Fizdale said the roster is set up to have a lot of big lineups.

The coach said pairing Mitchell Robinson and Bobby Portis up-front with Marcus Morris or Kevin Knox at the 3 and Barrett at the 2 would be one of the most sizeable quintets in the NBA.

“When you start talking about Kevin and Marcus Morris at the small forward, right there that makes you pretty big,’’ Fizdale said. “Look at Frank [Ntilikina] and Elfrid [Payton] — big [point] guards.’’