Tolerance & Derating Calculator
Convert percentage tolerances to real values. Essential for engineers and QA.
%
%
Minimum value90.000
Nominal100.000
Maximum value110.000
Total range (span)20.000
Absolute tolerance (±)±10.000
90Nominal: 100110
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Understanding Percentage Tolerance in Engineering
A ±10% tolerance means a component's actual value can be anywhere from 90% to 110% of its nominal (stated) value. A 100Ω resistor with ±10% tolerance can actually measure anywhere from 90Ω to 110Ω.
Standard Tolerance Bands (Electronics)
| Tolerance | Color Band | 100Ω Resistor Range | Relative Cost |
|---|---|---|---|
| ±20% | No band | 80–120Ω | $ |
| ±10% | Silver | 90–110Ω | $ |
| ±5% | Gold | 95–105Ω | $$ |
| ±2% | Red | 98–102Ω | $$$ |
| ±1% | Brown | 99–101Ω | $$$$ |
| ±0.1% | Violet | 99.9–100.1Ω | $$$$$ |
Each step in precision roughly doubles or triples the cost. A ±0.1% resistor can cost 50× more than a ±10% one.
Derating: Why "10% Off" Matters in Engineering
Derating means intentionally operating a component below its maximum rated value — typically by 10-20%. A capacitor rated for 50V used in a 40V circuit (20% derating) lasts significantly longer and is more reliable.
Common derating rules: capacitors 20%, power supplies 10-20%, wire ampacity 10-15% per additional conductor.
Frequently Asked Questions
Use the loosest tolerance that meets your requirements. ±10% is fine for most non-critical applications. ±1% or better for precision measurement, audio, and medical devices.
Most components drift with temperature. A ±5% resistor at 25°C may be ±8% at 85°C. Always check the temperature coefficient (tempco) spec and add it to your tolerance budget.
When multiple toleranced parts combine, their errors can add up (worst case) or partially cancel (statistical). Worst-case: three ±10% parts in series = ±30%. Statistical (RSS): ±17.3%.
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