Relay Coil Calculator
Calculate relay coil with this free online tool
Coil Characteristics
Coil Current
30.00 mA
I = V/R = 12V / 400Ω
Coil Power
360.00 mW
P = V²/R = 12² / 400
Recommended Transistor (BJT)
Min V_CE (collector-emitter)
>24.0 V
≥ 2× coil voltage
Min I_C (collector current)
>60.0 mA
≥ 2× coil current
Min Power Dissipation
>540 mW
≥ 1.5× coil power
Suggested transistors:
2N2222A, BC547, 2N3904
Flyback Diode
Min Voltage Rating
>24.0 V
Min Current Rating
>45.0 mA
Suggested: 1N4001, 1N4007 (connect cathode to V+, anode to collector)
Base Resistor (Arduino/MCU @ 5V)
Base Resistor Value
7.17 kΩ
Rb = (V_GPIO - V_BE) / (I_C_desired / h_FE)
Assumed h_FE = 100, V_BE = 0.7V
Nearest Standard Value
7 kΩ
Base resistor power: 2.58 mW
Quickly get accurate results with this free relay coil calculator. Everything runs locally in your browser for maximum privacy.
Key Features
Free relay coil calculator with instant results
No registration or signup required
Professional-grade relay coil calculator tool
Works on all devices and browsers
Privacy-first: all processing happens in your browser
Unlimited usage with no restrictions
How to Use Relay Coil Calculator
Enter Your Data
Input your values or data into the relay coil calculator tool fields
Configure Options
Adjust any optional settings or parameters for your specific needs
Get Instant Results
The tool automatically calculates and displays results in real-time
Copy or Export
Copy the results to clipboard or use them directly in your project
Repeat as Needed
Run the tool again with different inputs — unlimited usage, completely free
Use Cases
Use relay coil calculator for personal projects
Professional and academic applications
Quick reference and verification
Everyday productivity and convenience
Frequently Asked Questions
Is the Relay Coil Calculator free to use?
Yes, the Relay Coil Calculator is completely free with no registration required. Use it as many times as you need.
Do I need to create an account?
No account needed. All tools work instantly in your browser without any signup or login.
Is my data safe?
Absolutely. All processing happens locally in your browser. Your data is never sent to any server.
Does the Relay Coil Calculator work on mobile?
Yes, the tool is fully responsive and works on phones, tablets, and desktop computers.
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