Xray. The only way to know if your rib is truly broken is with an xray. This simple diagnostic test creates a picture of the rib cage which your physician can use to evaluate your pain. Sometimes it can be hard to see a fracture on xray. Typically these breaks take up to 6 weeks to heal.
Pain. Pain when you take a deep breath in, intense pressure when you push on the rib are major ways to identify a rib fracture.
Ct helps too. Xrays are good for screening but ct scans are more sensitive and can pick them up more reliably. This is really true with anterior fractures or costal cartilage injuries.