Relations used: V = I×R, P = V×I = I²R = V²/R. Enter the resistor's value plus whichever of voltage or current your circuit provides — the other electrical quantity and the dissipated power are computed automatically. Recommended rating applies a conservative 2× headroom over the actual dissipated power (e.g. 0.3W actual → use a 0.5W or larger resistor), which is standard practice for reliability and heat margin, especially in enclosed or high-ambient-temperature spots.