Calculator Input
Use the responsive field grid below. Large screens show three columns, smaller screens show two, and phones show one.
Example Data Table
| Nominal | Tolerance | Minimum | Maximum | Typical Use |
|---|---|---|---|---|
| 220 Ω | ±5% | 209 Ω | 231 Ω | General signal limiting |
| 1 kΩ | ±1% | 990 Ω | 1010 Ω | Precision analog biasing |
| 4.7 kΩ | ±10% | 4.23 kΩ | 5.17 kΩ | Non-critical pull-up networks |
| 100 kΩ | ±0.5% | 99.5 kΩ | 100.5 kΩ | Instrumentation dividers |
Formula Used
Rnom = Input Value × Unit Multiplier
ΔR = Rnom × (Tolerance / 100)
Rmin = Rnom - ΔRRmax = Rnom + ΔR
ΔRtemp = Rnom × (Tempco / 1,000,000) × |ΔT|
Rworst,min = Rmin - ΔRtempRworst,max = Rmax + ΔRtemp
P = I² × R
How to Use This Calculator
- Enter the resistor’s nominal value and choose Ω, kΩ, or MΩ.
- Add the tolerance percentage from the part marking or datasheet.
- Choose the band count to match common resistor coding practice.
- Enter tempco and expected temperature swing for drift analysis.
- Optionally enter a measured value, load current, power rating, and quantity for network checks.
- Press Calculate Tolerance to view min, max, worst-case range, power impact, graph, and export options.
Frequently Asked Questions
1. What does resistor tolerance mean?
Tolerance states how far the real resistance may vary from the printed nominal value. A ±5% resistor can legally measure anywhere within that ±5% band when new.
2. Is a lower tolerance always better?
Not always. Tight tolerance improves accuracy, but it may cost more. Many pull-up, LED, or non-critical loads work perfectly with wider tolerance parts.
3. Why does tempco matter?
Tempco shows how resistance shifts with temperature. In precision dividers, sensors, and analog references, temperature drift can matter almost as much as the original tolerance band.
4. What does the measured resistance field do?
It compares your real meter reading against the calculated nominal tolerance window and the expanded temperature-adjusted window, helping you screen questionable or stressed components.
5. How are series and parallel values estimated?
The calculator multiplies series resistance by quantity and divides parallel resistance by quantity. It also carries the tolerance range through those simple network arrangements.
6. Why is worst-case power higher than nominal power?
At a fixed current, higher resistance produces more heat because power follows I²R. The worst-case result uses the upper resistance edge after tolerance and thermal drift.
7. When should I choose four, five, or six bands?
Four-band parts are common for general work. Five-band parts often support tighter precision. Six-band parts usually add temperature coefficient information for better drift analysis.
8. When should a resistor be replaced?
Replace it when the measured value falls outside tolerance, shows thermal damage, exceeds power rating, or causes circuit behavior that depends on tighter resistance control.