We report a large piezoelectric constant (d(33)), 720 pC/N and converse piezoelectric constant (d(33)*), 2215 pm/V for 0.55(Ba0.9Ca0.1)TiO3-0.45Ba(Sn0.2Ti0.8)O-3 ceramics; the biggest value achieved for lead-free piezoceramics so far. The ceramic powders were calcined between 1050 degrees C-1350 degrees C and sintered at 1480 degrees C. The best properties were obtained at a calcination temperature (CT) of 1350 degrees C. The fitting combination of processing and microstructural parameters for example, initial powder particle size >2 mu m, ceramics density similar to 95%, and grain size similar to 40 mu m led to a formation of orthorhombic-tetragonal-pseudo-cubic (O-T-PC) mixed phase boundary near room temperature, supported by Raman spectra, pointed to the extremely high piezoelectric activity. These conditions significantly increase piezoelectric constants, together with high relative permittivity (epsilon(r)) >5000 and a low loss tangent (tan delta) of 0.029. In addition, the d(33) value stabilizes in the range of 400-500 pC/N for all samples calcined between 1050 degrees C and 1250 degrees C. The results entail that the (Ba,Ca)(Sn,Ti)O-3 ceramics are strong contenders to be a substitute for lead-based materials for room temperature applications.