What hemoglobin level is too low to go on a walk without getting light-headed?

Depends. If the hemoglobin decreases gradually, the body makes adjustments and a person may be able to conduct routine activities with a hemoglobin of as low as 5.0gm%. However, any one with low hemoglobin needs to be investigated to find the cause. Undetected cancer is a cause of anemia in adults, especially males. By the time you get light headed on a walk the hb is too low!