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Electronics Calculators

Quick maths for your builds — resistor colours, Ohm's law, LED resistors, dividers & battery life. Everything updates as you type.

Resistor Colour Code

4-band resistor → resistance value.

Band 1

Band 2

Multiplier

Tolerance

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Ohm's Law & Power

Enter any two — the rest are calculated.

Voltage (V)

Current (A)

Resistance (Ω)

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Fill any two fields above.

LED Series Resistor

Pick the resistor to drive an LED safely.

Supply (V)

LED forward (V)

LED current (mA)

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Voltage Divider

Vout = Vin × R2 / (R1 + R2).

Input voltage Vin (V)

R1 (Ω)

R2 (Ω)

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Battery Life

Rough run-time from capacity & average draw.

Capacity (mAh)

Avg current (mA)

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Capacitor Code

3-digit ceramic cap code → capacitance (104 = 100 nF).

Code (2 or 3 digits)

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Series / Parallel Resistors

Comma-separated values, in ohms.

Resistor values (Ω)

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RC Filter Cutoff

Low/high-pass −3 dB frequency. fc = 1 / (2πRC).

R (Ω)

C (µF)

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555 Timer (Astable)

Frequency, duty & period for a 555 oscillator.

R1 (Ω)

R2 (Ω)

C (µF)

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LiPo Charge (V → %)

Estimate battery % from pack voltage.

Pack voltage (V)

Cells

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// quick estimates for hobby builds — always double-check against your part's datasheet.