E-Series Preferred Value Finder

Snap any ideal value to the nearest real E3–E192 part and see the error you inherit by doing so.

Example: The nearest E24 value to 3.3 kΩ is 3.3 kΩ, 0% away.

Inputs

Ideal value

Engineering shorthand works: 4k7, 2.2k, 100n.

Series

Unit

Result

Nearest E24

3.3 kΩ

Error against ideal: +0%
Series tolerance: ±5%
Worst-case low: 3.135 kΩ
Worst-case high: 3.465 kΩ
Values per decade: 24

3.3 kΩ is already an E24 value — no compromise needed.
The rounding error is far smaller than the tolerance. Moving to a finer series would not make the circuit more accurate — buying tighter-tolerance parts would.

E24 values around 3.3 kΩ

Value	Error vs ideal	Worst-case low	Worst-case high
2.4 kΩ	-27.27%	2.28 kΩ	2.52 kΩ
2.7 kΩ	-18.18%	2.565 kΩ	2.835 kΩ
3 kΩ	-9.09%	2.85 kΩ	3.15 kΩ
3.3 kΩ	+0%	3.135 kΩ	3.465 kΩ
3.6 kΩ	+9.09%	3.42 kΩ	3.78 kΩ
3.9 kΩ	+18.18%	3.705 kΩ	4.095 kΩ
4.3 kΩ	+30.3%	4.085 kΩ	4.515 kΩ

The series compared

Series	Per decade	Tolerance	Nearest to 3.3 kΩ	Error
E3	3	±40%	2.2 kΩ	33.33%
E6	6	±20%	3.3 kΩ	0%
E12	12	±10%	3.3 kΩ	0%
E24	24	±5%	3.3 kΩ	0%
E48	48	±2%	3.32 kΩ	0.61%
E96	96	±1%	3.32 kΩ	0.61%

Formula

each series divides a decade into N logarithmically spaced steps

Calculations follow IEC 60063.

Worked example

The nearest E24 value to 3.3 kΩ is 3.3 kΩ, 0% away.

E24 divides each decade into 24 logarithmic steps
ratio between adjacent values = 10^(1/24) ≈ 1.1007
10.1% apart
Logarithmic spacing means the percentage gap between neighbours is constant across the whole range.
nearest = the series value closest to the ideal
3.3 kΩ → 3.3 kΩ
0% error

Frequently asked questions

Why do resistors come in odd values like 4.7 kΩ and 6.8 kΩ?

They are logarithmically spaced so each value's tolerance band just meets its neighbour's, covering the whole range with no gaps and no waste. E24 divides each decade into 24 steps about 10% apart — which matches 5% tolerance parts exactly.

What is the difference between E12, E24 and E96?

How finely each decade is divided, and therefore what tolerance they pair with. E12 has 12 values per decade for 10% parts, E24 has 24 for 5%, and E96 has 96 for 1%. A finer series only helps if you also buy the tighter tolerance.

Does rounding to a preferred value hurt my circuit?

Usually far less than the part tolerance does. Snapping to the nearest E24 value costs at most about 5%, and a 5% resistor already varies by that much between parts. Fix the tolerance before worrying about the rounding.

Can I get any value by combining resistors?

Yes — two in series add, two in parallel give something below both. It is a reasonable way to hit an unusual value, but it doubles the part count and the tolerances compound, so it is rarely worth it unless the value genuinely matters.

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