The average distance to Mars from Earth is 140,000,000 miles or 225,000,000 kilometers. However, this value varies because the Earth's orbit around the sun is smaller than Mars' orbit.
Earth is the third planet from the sun and Mars is the fourth. Each planet orbits the sun at differing speeds. Earth has an inside track, so it moves around the sun more quickly. Both planets also have elliptical orbits, so the distance between Earth and Mars constantly varies.
Theoretically, the closest that both planets could come together is when Mars is at its nearest point to the sun and Earth is at its farthest. When that happens, the planets would be 33,900,000 miles, or 54,600,000 kilometers, away from each other. However, when both planets are at their farthest from the sun, they can be 250,000,000 miles, or 401,000,000 kilometers, away from each other.