Right now, transferring Chase Ultimate Rewards to Marriott points gives a 50% bonus, raising the ratio from 1:1 to 1:1.5. The offer runs until Dec. 24.
But personally, I think Marriott points are worth only around 0.7, while UR points are worth about 1.6. If you don’t need to top up points for hotel bookings or to redeem for bigger rewards, this offer isn’t very meaningful.