Resistor Calculator
Ohm's law from any two of V, I, R and P — plus the resistor you can actually buy.
What is Resistor?
A calculated resistance is almost never a purchasable one. 219.4 Ω does not exist; 220 Ω does, and that is the difference between an Ohm's-law exercise and choosing a part. This page does both: it solves V = I·R and P = V·I for whichever two quantities you supply, then snaps the answer to a preferred value and works out the power the resistor will actually dissipate.
How it works
The four quantities are related by two equations, so any two of them fix the rest — which pair you gave decides the arrangement, and the working shows the substitution used. The resistance is then matched to the E12 (10%), E24 (5%) or E96 (1%) preferred series, rounded up, down or to the nearest, and reported with the current or voltage that value really produces. Dissipation is P = I²R at the solved current, and the page names the smallest standard power rating with a 2× margin, because a resistor run at its rating runs hot.
- Enter your input. Type or paste your input into the field above — the tool responds instantly.
- Review the result. Output updates live as you type. Everything runs entirely in your browser.
- Copy or download. Use the Copy button to grab the result, or Download to save it as a file.
Examples
Realistic sample
Type or paste any realistic input — the tool computes the result locally and instantly.
Common mistakes
Expecting a server round-trip
Nothing is uploaded — every tool in this category runs entirely in your browser.