The exact answer varies as both Mars and our planet are constantly moving along their own orbits around the Sun.
Mars is about 225 million km or 140 million miles from Earth. This is calculated by averaging the variability in distances along its orbit.
To most people (myself included) those are just numbers. Big numbers — and really not even all that big in an astronomical sense. So to give a sense of what it means to cross the distance between here and Mars, interactive designer David Paliwoda created a web page that illustrates the scale involved quite nicely. http://www.distancetomars.com/
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