Ohm's law and DC power solver

Assumptions to check

• Steady-state DC conditions.
• An ideal resistive element with no temperature coefficient.
• No transient, pulse, or wiring-loss model.

What this solves

Ohm’s law is useful when a DC design decision starts with two known quantities and needs the other two. The same relationship can answer a simple LED-resistor question, a sensor-divider loading check, or a first-pass power estimate. The useful answer is not only the number. It is whether the number places an ordinary resistor in a sensible operating region.

This tool keeps voltage, current, resistance, and power as a single consistent set. Choose the pair you know, then compare the resulting dissipation with an optional resistor rating. It does not silently treat a nominal result as a temperature, surge, or qualification result.

Worked example

With 12 V across 1 kΩ, current is 12 mA and dissipation is 144 mW. A 0.25 W resistor carries that nominal load, but the margin is modest once tolerance, ambient temperature, enclosure heat, or pulse behavior matter. The calculation is exact for the stated ideal model; the component decision is not complete until its data sheet conditions are checked.

Limits and next checks

Do not use this page to approve a resistor for fault energy, repetitive pulses, mains wiring, or safety-critical work. Those cases need the appropriate part ratings and system review. If the source includes other resistors or loads, reduce the network first. If the result selects a part value, use the preferred-value selector and then perform the relevant rating and tolerance checks.

Common mistakes

• Treating a nominal resistor wattage as a full-load design target.
• Forgetting that a divider or parallel load changes the current.
• Using a DC calculation as a pulse-energy or safety analysis.

Model limit and handoff

Verify the selected part against its data sheet, operating temperature, tolerance, pulse profile, and the measured circuit when nonideal behavior matters.

FAQs