Standard Resistor Value Calculator (Nearest E12 / E24 / E96 & Best Two-Resistor Combination)
Find the nearest standard resistor values in the E12, E24 and E96 series to any calculated resistance with the percentage error, the best series or parallel pair of E24 resistors to hit the target more closely, and the tolerance band that makes the effort worthwhile.
How it works
E-series values: E12 = 10^(n/12), E24 = 10^(n/24), E96 = 10^(n/96) rounded to standard tables · nearest = minimum |log(value ÷ target)| across decades · series pair: R₁ + R₂; parallel pair: R₁R₂ ÷ (R₁ + R₂); best pair found by exhaustive search
Resistors come in preferred values spaced so that each is roughly one tolerance band from the next — 12 per decade for 10% parts, 24 for 5%, 96 for 1%. A calculated value almost never lands on one, so you pick the nearest and check whether the error matters, or build the value from two resistors in series or parallel. This calculator gives the nearest value in each series with its error, the best two-resistor combination in the series you have, and a reality check: two loose-tolerance parts in series are still loose, so precision comes from tighter parts, not from clever combinations.
Worked example
A calculated 1,050 Ω: nearest E12 is 1.0 kΩ (−4.8%), E24 1.1 kΩ (+4.8%), E96 1.05 kΩ exactly. With 5% parts the single value is off by as much as its own tolerance, so 300 Ω + 750 Ω in series (exactly 1,050 Ω) or 1.1 kΩ ∥ 24 kΩ (1,052 Ω) hits it — but the pair is still a 5% pair; a single 1% 1.05 kΩ is the clean answer.
Frequently asked questions
Why are resistor values 1.0, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, 8.2?
They are the 12th roots of 10, rounded — each is about 21% above the last, so 10% resistors of adjacent values just cover the decade without gaps. E24 halves the spacing for 5% parts; E96 is for 1%.
Does putting two resistors in series improve accuracy?
It lets you hit a nominal value between standard ones, but the tolerance does not improve — two 5% resistors in series are still within about 5% of the combined nominal. Use 1% or 0.1% parts when accuracy matters, or add a trimmer.
How do I read an E96 code like "4991"?
Three significant figures and a multiplier: 4991 = 499 × 10¹ = 4.99 kΩ. On very small SMD parts a two-character EIA-96 code is used (a two-digit index into the E96 table plus a letter for the multiplier).
Related calculators
Values follow the IEC 60063 preferred-number series; check the exact parts your supplier stocks.