Question 1

What are E-series preferred values?

Accepted Answer

E-series are the standardised sets of preferred numbers defined in IEC 60063 for resistors, capacitors and other components. Each series (E6, E12, E24, E48, E96, E192) splits every decade into equal logarithmic steps, so the values repeat every factor of ten — for example 4.7 Ω, 47 Ω, 470 Ω and 4.7 kΩ all belong to the same E24 step.

Question 2

How is the nearest preferred value chosen?

Accepted Answer

The calculator scales the official IEC 60063 base values across the decades around your target and selects the one with the smallest absolute difference. It also reports the values immediately below and above the target so you can decide whether rounding up or down suits your circuit better.

Question 3

Which E-series should I use?

Accepted Answer

Match the series to the tolerance you need. E6 (±20%), E12 (±10%) and E24 (±5%) cover general-purpose carbon-film parts; E48 (±2%), E96 (±1%) and E192 (±0.5%) cover precision metal-film resistors. A finer series gives a smaller worst-case error but the parts cost more.

Question 4

Why are E6, E12 and E24 values rounded?

Accepted Answer

The raw geometric steps would give awkward numbers, so IEC 60063 rounds the lower series to convenient two-figure values — for instance the E24 step that the geometric series puts near 26.1 is defined as 27. The E48, E96 and E192 series use the exact three-figure table from the standard, so this tool hard-codes the official tables rather than recomputing the geometric values.

Question 5

Does the nearest preferred value account for component tolerance?

Accepted Answer

No. The preferred value is only the nominal (marked) value. A real part may sit anywhere within its tolerance band — ±5% for E24, ±1% for E96 and so on — and capacitors and resistors also drift with temperature and applied voltage. Treat the percent error shown here as a design starting point, not a guaranteed value.

E-Series Preferred ValueCalculator

E-Series Preferred Value
Calculator