Calculator
Example Data Table
| Target | Series | Expected Nearest Value | Use Case |
|---|---|---|---|
| 4.7 kΩ | E12 | 4.7 kΩ | Pull-up resistor |
| 9.8 kΩ | E24 | 10 kΩ | Voltage divider |
| 324 Ω | E96 | 324 Ω | Precision biasing |
| 68 kΩ | E6 | 68 kΩ | General filtering |
Formula Used
The calculator compares the target resistance with preferred values from the selected E series.
Normalized E value: Rn = 10k/N, where N is the E series number.
Candidate value: R = Rn × 10d, where d is the decade.
Error percent: Error = ((R - Target) ÷ Target) × 100.
Tolerance range: Minimum = R × (1 - Tolerance ÷ 100). Maximum = R × (1 + Tolerance ÷ 100).
Current: I = V ÷ R. Power: P = V² ÷ R.
How To Use This Calculator
Enter the target resistance first. Select ohms, kilo-ohms, or mega-ohms. Choose the E series used by your parts stock or design rule. Enter tolerance if you need a custom value. Leave it blank only when you want to use the usual series tolerance. Add circuit voltage when you want current and wattage estimates. Press Calculate to see the best match above the form. Use CSV for spreadsheets. Use PDF for simple reports.
Resistor E Series Guide
Why Preferred Values Matter
Resistor values are not random. They follow preferred number groups called E series. These groups help manufacturers cover each decade with useful steps. A decade means one power of ten. For example, 10 Ω to 100 Ω is one decade. The same pattern repeats through kilo-ohms and mega-ohms.
Choosing The Right Series
E6 and E12 suit rough circuits. They are common in simple filters, indicators, and pull-up networks. E24 gives closer choices for everyday design. E48, E96, and E192 support tighter work. They help when gain, bias, timing, or divider output must stay near a target.
Understanding Error
This calculator checks how far each preferred value is from your entered target. The error may be positive or negative. A positive value is higher than the target. A negative value is lower. The absolute error shows closeness without direction. The nearest value has the smallest absolute error.
Tolerance Range
Real resistors vary. A 10 kΩ part with five percent tolerance may measure from 9.5 kΩ to 10.5 kΩ. That range matters in analog circuits. It also matters in sensor dividers and reference networks. Lower tolerance parts reduce uncertainty, but they often cost more.
Power Check
Resistance selection is not only about ohms. Power must also be safe. When voltage is entered, the tool estimates current and heat. It then applies your safety factor. This helps select a wattage rating with margin. Use a higher factor for warm enclosures or continuous loads.
Band Names
The band output gives the resistor color code names. E24 and lower values use two main digits. Higher precision series use three main digits. The final tolerance band depends on the tolerance you enter. Always confirm unusual values with a datasheet or meter.
FAQs
What is a resistor E series?
An E series is a preferred number set for resistor values. It divides each decade into fixed steps. Common sets include E12, E24, E96, and E192.
Which E series should I use?
Use E12 for rough designs. Use E24 for general work. Use E96 or E192 when the circuit needs closer resistance values and tighter control.
Why is the nearest value not exact?
Standard resistors are sold in preferred values. Your target may fall between two values. The calculator selects the closest available value from the chosen series.
What does tolerance mean?
Tolerance is the allowed variation around the marked resistor value. A five percent 100 Ω resistor can measure between 95 Ω and 105 Ω.
Can this calculator estimate power?
Yes. Enter circuit voltage. The calculator estimates current, power dissipation, and a suggested minimum wattage using your safety factor.
What is absolute error?
Absolute error is the error size without direction. It ignores whether the preferred value is above or below the target.
Why are band names included?
Band names help identify the physical resistor marking. They are useful when selecting or checking through-hole resistors in a parts box.
Should I always pick the nearest value?
Not always. Sometimes a lower or higher value is safer for current, gain, timing, or bias. Review the circuit goal before final selection.