I'm selling my stock wheels and tires. How do I Find what percentage of tire tread I have left?

Thanks

 

I just made an eye ball estimate on the tread when I sold mine. If you want to be scientific, use a ruler to measure a new tire and your old tires and do the math. Typical tires have about 1/5-1/4" of depth in the center I think. Sometimes, it's also good to provide the mileage on the tires beside a % also. Also, pictures will help in selling too.