Will 275-65-18 tires fit on my rim that currently has 265-70-16 tires on them?

I have old 265-70-16 tires on my truck and was given four 275-65-18 tires, I was just wondering if they will fit on my rim. Any help is greatly appreciated. I've tried tire calculator websites but I cant seem to get a simple answer anywhere...I know apparently I'd be going slightly faster than my speedometer would say.