Sometimes a blood clot will not show any symptoms so you may not know if you have a blood clot in your leg without seeing a doctor.
But if the blood clot is severe enough then usually you'll have swelling of your entire leg along with severe pain or you may also just experience minor calf swelling with just minor pain.
If you think you have a blood clot or you suddenly experience welling in your legs or arms you should always see a doctor or get to the emergency room to get checked out because a blood clot can lead to a heart attack and even death if not treated.