CalcFormula is a free calculator site for construction and electrical work — over 300 tools covering concrete, framing, slope, drainage, steel weight, and pipe sizing. What makes it different: every formula is checked against real sources (ACI, IBC/IRC, ASTM, ASME) instead of copied from other sites, and many tools go further than typical competitors — multiple shapes, flexible unit entry, reverse-solve modes — instead of one rigid input path. No signup, no paywall, just the math done right.