Shelton popped the question to his longtime love last fall.
The "Minimum Wage" singer recently appeared on the Apple Music radio show Party Barn Radio With Luke Bryan where he opened up to his pal about his desire to shed weight ahead of his wedding day to Stefani, 51.
"Scale of 1 to 10, Blake Shelton, [will you] you lose 20 pounds for your wedding?" Bryan asked his pal.
"I feel like if I say 10 I have to do it, so 10," Shelton replied. "It's out there now so I can't let people down."
About his quarantine weight gain, Shelton admitted that his new look isn't making him feel great.
"I've readjusted all the mirrors in the house so they look like when you're taking a selfie from up above because I can't even stand to look at myself in the mirror," he quipped. "So I've rearranged them where they're kind of angled down looking down at me and it's not so bad."
And while he's not so confident about his look, Shelton does seem self-assured that Stefani will make it down the aisle to be his bride.
"I'm going with a 10, buddy. I've got confidence," he insisted when asked whether Stefani would go through with the wedding.
Shelton also said that he'd been dodging Bryan's texts because of Stefani's adherence to COVID-19 safety procedures.
"She's very strong about this quarantine thing, which is great... She's the only person I get to see so, that's it. No buddy hanging out time," Shelton said. "When you're a prideful, stubborn guy like myself for me to text you back and say, 'Man, Gwen won't let me go.' That's tough. It's embarrassing."
Back in September 2020, Shelton opened up about his new appearance on The Ellen DeGeneres Show, sharing that Stefani had dyed his hair grey.
"I actually really liked it. I would have really liked it better had I not gained 117 pounds during quarantine," he joked at the time. "I thought it made me look younger, but I was still just as fat. Now I'm actually trying to lose weight. I'm not opposed to having her color my hair again. I don't care. If it makes her happy, I'm cool with it."