Resistor Power Rating Calculator NZ

This calculator works out how much power a resistor dissipates as heat, and the power rating you should choose to use it safely. Every resistor turns some electrical energy into heat as current flows through it, and if that heat exceeds what the resistor is built to handle, it overheats, drifts in value, or burns out. Resistors are therefore sold with a power rating, the maximum they can safely dissipate, and choosing one with an adequate rating is a basic but essential part of circuit design that beginners often overlook, leading to scorched components. This calculator helps you get it right. You enter the resistance and the current flowing through it, and the calculator returns the power the resistor will dissipate, the voltage across it, and a recommended power rating that includes a safety margin, along with the current for reference. The results update as you type. Use it for electronics design, for choosing resistors, or for physics study. The power dissipated is the current squared times the resistance, equivalently the voltage across the resistor times the current, and the voltage itself is the current times the resistance by Ohm's law. The recommended rating doubles the dissipated power, a common rule of thumb that keeps the resistor running well within its limits, cooler and more reliable, since running a component near its maximum rating shortens its life and risks failure. Standard resistor power ratings come in steps such as an eighth, a quarter, a half, one and two watts, so you would round the recommendation up to the next standard size. Knowing the dissipation also tells you how much heat the circuit must shed, which matters in dense or enclosed designs. Sizing resistors properly is a small step that prevents a surprisingly common cause of circuit failure.

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Power = current² x resistance = voltage x current. Recommended rating doubles the dissipation for safety. Round up to a standard size (1/8, 1/4, 1/2, 1, 2 W).