How do i know if i broke a rib?

Only X-Ray can tell: Rib injuries (whether broken or not) are notoriously bothersome, because the chest wall moves with every breath, so it is not possible to rest the injured area. Only an x-ray can tell whether a rib is broken or not; your doctor may be able to order one for you at a local hospital or freestanding radiology office, or else you can go to an urgent care clinic.

Exam: An x-ray will be negative early after a rib fracture. A cat scan will be too if not severe. Typically point tenderness over the rib is enough to diagnoses a rib fracture if the appropriate mechanism of injury has occurred. For example, if it started hurting after you woke up, it's not a rib fracture. If you wrecked your car of fell off a ladder then it's likely a fracture.