Look along the rim of your tire. You should be able to find a group of numbers separated by slashes and/or dashes. There are two general types of tire sizing, metric and english. Most street and dirt bikes use metric sizes. A metric size will look like 100/90-19. Most ATVs use english sizes, english size will look like 35x10-15.
Sometimes you just need one. Maybe you popped it or got into a cycle of wearing one before the other so if you ever need just one front tire for your dirt bike grab your pick from our wide selection. Generally, you'd replace the same brand but whatever you decide, find all the best dirt bike front tire brands for riding in sand, enduro, trails and the Motocross track at MotoSport. Use the tire finder above to determine the right fit for your ride. if you need help, give a gearhead a call at 1-888-676-8853 and get answers to common questions and any other advice you need.
You won't get a pithy answer right here because the instructions on how to change a front dirt bike tire exceeds the space allowed. As such, check out How To Change A Dirt Bike Tire with near step-by-step instructions as well as links to all the tools you need.