Median price per square foot for Johns Creek is quoted around $495. Can I just multiply that by my square footage?

A single quoted price-per-square-foot figure should not be multiplied directly against your square footage, since condition, lot, upgrades and exact location swing that number street by street within Johns Creek, and this site cannot confirm any published average as current. Two homes with identical square footage can sell far apart once finishes, lot quality and school zone are factored in. A comparative market analysis built from recent closed sales on comparable homes nearby gives a reliable number instead.