Each straight on a standard 400m outdoor track is 84.39 meters long.
World Athletics' standard design joins two 84.39-meter straights with two semicircular bends. Each bend has a radius of 36.50 meters, producing a track whose measured running line in lane one is approximately 400 meters. The precise calculation is why the straights are shorter than the 100 meters many people casually expect.
The 100-meter race is run entirely on a straight, but its start and finish markings do not mean that a 400-meter oval has 100-meter straights. On a standard oval, most of the lap distance comes from the curved sections. Track geometry and the exact measurement line also explain why diagrams can show slightly different overall dimensions.
Lane one is the reference lane for the standard 400-meter distance. Outer lanes are staggered because their curves have larger radii, preventing runners farther from the center from covering extra distance.