Ragnow's deal is worth $13.5 million per season and will run through 2026, NFL Network's Tom Pelissero reports. The extension contains $25.5 million fully guaranteed at signing and $42 million in total guarantees, according to NFL Network's Mike Garafolo.
The Los Angeles Chargers' Corey Linsley previously topped the center market in March after he signed a five-year deal worth $12.5 million annually.
Ragnow was PFF's second-ranked center last season after allowing zero sacks and just nine pressures in 14 games. He also earned his first Pro Bowl nomination and second-team All-Pro honors.
The Lions selected the 24-year-old in the first round of the 2018 NFL Draft. Ragnow has made 45 career starts in three seasons.