Resistors and capacitors are made in standard value series, not in every possible value. When a calculation gives 4.9 kΩ or 37.4 kΩ, you need to know which real parts are closest. This calculator finds the nearest standard value in any of the common series, plus the values on either side, so you can choose between rounding up and rounding down.
How to use it
- Enter the value you calculated or measured. The unit is only a label: the same series apply to capacitors, so you can enter 3.9 µF as
3.9with any unit. - Choose the series that matches the tolerance you will buy.
- Read the closest value, the neighbours and the error.
The E-series
| Series | Values per decade | Typical tolerance | Where you see it |
|---|---|---|---|
| E6 | 6 | ±20 % | Electrolytic and some ceramic capacitors |
| E12 | 12 | ±10 % | Capacitors, older resistors |
| E24 | 24 | ±5 % | General-purpose resistors, 3-digit SMD codes |
| E48 | 48 | ±2 % | Less common |
| E96 | 96 | ±1 % | Precision resistors, feedback dividers, 4-digit and EIA-96 codes |
Each series spaces its values evenly on a logarithmic scale, so neighbouring values differ by roughly the same percentage across the whole range.
Worked example: a feedback resistor
You calculate that a regulator needs a 37.4 kΩ top resistor. In E24 the neighbours are 36 kΩ and 39 kΩ — about 4 % off, which would shift the output voltage noticeably. In E96, 37.4 kΩ exists exactly. That is why regulator feedback networks are almost always built from 1 % E96 parts, and why a replacement must come from the same series. The output voltage calculation is in Regulator Feedback Resistor Calculator.
When the original value is unusual
If the schematic shows a value that is not in any series, check for a typo — or for a resistor made of two parts in series or parallel; Resistors in Series and Parallel Calculator helps there. Reading the values printed on parts is covered in SMD Component Marking Codes: How to Identify Unknown Parts.
FAQ
Should I round up or down?
It depends on the job. For a current-limiting resistor, round up to stay below the target current. For a divider, choose the closest and check the resulting voltage.
Does every E24 value exist in E96?
Not all of them. E96 contains many but not all E24 values, so check the series your supplier stocks.
Do capacitors use the same series?
Yes, usually E6 or E12 because capacitor tolerances are wider.