Component Derating Calculator
Apply linear temperature derating to get safe operating power.
How to Use
- Enter rated power, rated temp, max temp (where P=0), and actual operating temp.
Show Work
Formulas
History of Component Derating
Derating as a formal reliability practice emerged from US military electronics procurement in the 1950s. The 1957 Department of Defense MIL-HDBK-217 ("Reliability Prediction of Electronic Equipment") established the first standardized derating tables — resistors, capacitors, semiconductors — based on the Arrhenius rule that chemical reaction rates (including insulation breakdown, electrolyte dry-out, and dopant diffusion) roughly double for every 10°C increase in temperature.
Aerospace adopted aggressive derating after the failure-mode analyses of the 1960s space program. A resistor rated 0.5 W at 70°C might be used at only 0.15 W (30% derate) in a spacecraft at 25°C — trading off board area for hundreds-of-thousands of failure-free mission hours. Commercial electronics typically derate 50-70%, industrial 40-60%, consumer products 20-40% — a spectrum that shows up directly in BOM cost per unit.
The linear derating curve is a simplification. Real components have nonlinear thermal behavior: electrolytic capacitors follow Arrhenius (half-life doubles every 10°C below max temp), film capacitors are nearly flat below max, and power semiconductors derate steeply above their breakpoint due to internal thermal resistance. For precision reliability, derate using the manufacturer's published curve, not a straight-line approximation.
About This Calculator
Enter the component's rated power, the temperature at which that rating applies, the maximum temperature at which power must drop to zero, and the actual operating temperature. The tool computes allowed power as a linear interpolation: P(T) = P_rated × (T_max − T) / (T_max − T_rated) above the breakpoint, or P_rated below it.
For a typical 0.25 W resistor rated at 70°C with T_max = 155°C, operating at 100°C gives P_allowed = 0.25 × (155 − 100)/(155 − 70) = 0.162 W. To maximize reliability, apply an additional 2× safety margin beyond the datasheet curve — i.e., use 0.08 W even though 0.162 W is allowed. Everything runs client-side; no values leave your browser.
About the Component Derating Calculator
Meet the Component Derating Calculator: a free, no-fuss tool for electronics and circuit design with nothing to install and no sign-up. Apply linear temperature derating to get safe operating power.
How it works
Put each value in its box and read the answer as you go. Because it recalculates live, you can play with the inputs to see how each one moves the result — handy for checking your own working or planning ahead. Everything happens on your device, so it is fast and private.
Want the deeper story? The Knowledge Base explains the ideas behind the tools in more detail.
Frequently Asked Questions
Why derate?
Components rated at a specific ambient; higher ambient → hotter internal → reduced safe power.
How do I use the Component Derating Calculator?
Simply type your numbers and read the result, which refreshes the instant you change something. There is nothing to submit and nothing to wait for.
Do I need to install or sign up for anything?
Not at all — it runs in the browser with nothing to install and no account. After it loads once, it even works without an internet connection.
Is my information private?
Yes. Everything happens in your browser. Nothing you type is sent to a server or saved anywhere.
Common Use Cases
Resistors
Typical: rated at 70°C, 0W at 155°C.
Caps
Rated at 85 or 105°C.
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