What is the difference between Fe500 and Fe550 TMT bars in the estimate?

Fe500 and Fe550 refer to the yield strength grade of the TMT bar, with Fe550 offering higher strength that can sometimes allow slightly less steel by weight for the same structural demand, though the choice depends on your structural engineer's design rather than a simple swap. The calculator lets you see directional cost differences between grades, but grade selection for your actual structure should follow the structural drawings, not a preference chosen independently at the estimate stage.