E-Series Preferred Values

Why resistors come in these odd numbers

Standard component values are not arbitrary and they are not evenly spaced. Each E-series divides every decade into a fixed number of steps spaced logarithmically, so that consecutive values differ by a constant percentage rather than a constant amount. E12 uses twelve steps per decade, so each value is about 21% above the last; E24 uses twenty-four steps, about 10% apart.

The spacing is chosen to match the tolerance. With ±10% parts, the tolerance bands of adjacent E12 values just touch — 10 kΩ covers 9 kΩ to 11 kΩ, 12 kΩ covers 10.8 kΩ to 13.2 kΩ — so every possible resistance is covered by some part, with minimal wasteful overlap. That is the entire logic of the system: the number of values per decade is set by how accurately the parts can be made. It is why you can buy a 4.7 kΩ ±5% resistor and a 4.99 kΩ ±1% one, but not a 4.7 kΩ ±1%.

The series are defined in IEC 60063 and apply to resistors, capacitors, inductors and Zener diodes alike.

Which series will you actually find in stock?

• E24 — the workhorse for ±5% carbon and thick-film resistors. If you are prototyping, your parts drawer is E24.
• E96 — the standard for ±1% metal-film and thin-film parts, and what you will use for anything precision. This is where 4.99 kΩ, 2.21 kΩ and 10.2 kΩ come from.
• E12 — still common for capacitors, where tolerances are looser and the extra values would be meaningless.
• E6 — electrolytic capacitors, mostly. A ±20% electrolytic does not justify finer steps.
• E48 and E192 — real but much less widely stocked. Check availability before designing one in; a distributor may list the value and hold none of it.

Getting a value that isn't in any series

If your calculation lands somewhere awkward, you have four options, roughly in order of preference:

1. Round to the nearest standard value and check the error matters. Most of the time it does not. A pull-up resistor does not care whether it is 4.7 kΩ or 5.1 kΩ.
2. Move to a finer series. E96 gets you within 0.5% of any target, which is enough for almost everything.
3. Combine two parts. Series addition or parallel combination reaches values no single part offers — 10 kΩ in parallel with 100 kΩ gives 9.09 kΩ. The cost is board area, an extra line on the BOM, and doubled tolerance stacking.
4. Redesign so the value doesn't matter. Often the cleanest answer. If a divider ratio is critical, use a trimmer or a matched array; if a timing constant is critical, calibrate in firmware rather than chasing a resistor.

The tables

Every series repeats across all decades. A value of 47 in E24 means 4.7 Ω, 47 Ω, 470 Ω, 4.7 kΩ, 47 kΩ and so on. E48, E96 and E192 are conventionally written with three digits, so 4.99 kΩ appears as 499.

E6 — 6 values per decade, ±20%

E12 — 12 values per decade, ±10%

E24 — 24 values per decade, ±5%

E48 — 48 values per decade, ±2%

E96 — 96 values per decade, ±1%

E192 — 192 values per decade, ±0.5% and tighter

Frequently asked questions

Why are resistor values like 4.7 kΩ and 6.8 kΩ instead of round numbers?

Because the standard series are spaced logarithmically, not linearly. Each E12 value is about 21% above the previous one, so the tolerance bands of adjacent values just touch and every possible resistance is covered without wasteful overlap. Round decimal numbers would leave gaps in some places and heavy overlap in others.

What is the difference between E12, E24 and E96?

The number of values per decade: E12 has 12, E24 has 24, E96 has 96. More values means finer steps, which is only useful if the parts are accurate enough to tell them apart — so E12 pairs with ±10% tolerance, E24 with ±5%, and E96 with ±1%.

Which resistor series should I design with?

E24 for general-purpose work and anything you want to buy cheaply in small quantities, E96 for precision analogue, dividers, references and gain-setting networks. E48 and E192 exist but are far less widely stocked — check availability before committing.

How do I get a value that isn't a standard one?

Round to the nearest standard value and check whether the error actually matters — usually it does not. If it does, move to E96, or combine two resistors in series or parallel. Combining costs board space and stacks tolerances, so treat it as a last resort.

Do capacitors use the same E-series?

Yes, but usually coarser ones. Ceramics are typically E12 or E24, and electrolytics are commonly E6 or E3 because a ±20% part cannot meaningfully distinguish finer steps.

What does the E in E-series stand for?

It comes from 'exponential', reflecting the logarithmic spacing. The series are formally defined in IEC 60063 and the number after the E is simply how many steps fill one decade.