How tall is that tree? If it falls down will it hit my house? If you want to figure the height of a tall tree do this: take a yardstick out into your yard and measure its shadow. Find the time of day when the shadow of the yardstick is 36". When the shadow of the yardstick is 36", you know that everything's shadow is equal to its true height; therefore, all you need to do is measure the tree's shadow to know its full height!