Ohm's law calculator
For a known pair of voltage, current and resistance, including power calculation.
21 tools
Electronics calculators
Calculations for people who solder and build: the series resistor for an LED, Ohm's law solved in any direction, inverter draw and battery run time. Each calculator checks the physics — it will not accept a forward voltage above the supply, for instance.
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Battery charge time calculator
How long a battery takes to charge at a given current.
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Electronics calculators
Battery runtime calculator
How long a battery lasts under a given load.
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Electronics calculators
Battery series and parallel calculator
Pack voltage, capacity and energy from the wiring arrangement.
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Electronics calculators
Capacitor charge and energy calculator
Charge, voltage or capacitance of a capacitor, plus the stored energy.
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Electronics calculators
Capacitors in series and parallel calculator
Total capacitance of capacitors wired in series or in parallel.
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Electronics calculators
Coaxial cable impedance calculator
Characteristic impedance of coax from the conductor and shield diameters and the dielectric.
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Electronics calculators
Headphone power calculator
Estimated SPL and required RMS voltage/current from sensitivity at 1 mW.
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Electronics calculators
Inverter power calculator
Battery draw of an inverter from its output power and efficiency.
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Electronics calculators
kVA to kW calculator
Converting apparent power to active power through the power factor.
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Electronics calculators
LC resonant frequency calculator
Tank circuit frequency from inductance and capacitance.
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Electronics calculators
LED resistor calculator
Series resistor for an LED, with the power it will dissipate.
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Electronics calculators New
NE555 astable timer calculator
Frequency, period and duty cycle of an NE555 multivibrator from two resistors and a capacitor.
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Electronics calculators
Ohm's law calculator
Voltage, current or resistance from the known pair, with power dissipation.
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Electronics calculators
RC circuit calculator
Cutoff frequency and time constant of a resistor with a capacitor.
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Electronics calculators
Resistor colour code calculator
Resistor value from its four colour bands, with the tolerance range.
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Electronics calculators
Resistor network calculator
Total resistance of a circuit in series and in parallel.
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Electronics calculators
RMS voltage calculator
Convert between peak, peak-to-peak and RMS voltage for sine, square and triangle waves.
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Electronics calculators
Single-phase power calculator
Active, apparent and reactive power of a single-phase circuit, or current from power.
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Electronics calculators
Transformer turns ratio calculator
Turns, voltages and currents of an ideal transformer.
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Electronics calculators
Voltage divider calculator
Output voltage, current and per-leg power of a two-resistor divider.
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Electronics calculators
Voltage drop calculator
Voltage lost along a cable run, from its length, cross-section and material.
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Which calculation to choose
LED resistor calculator
For an LED resistor: use supply voltage, forward drop and target current.
What to prepare
Take component parameters from its documentation. Enter current in the unit selected on the form; use amps for a manual formula check. Check the voltage across the resistor itself.
Common mistake
Resistor power uses its own voltage drop, not the full supply. A numerical result does not certify circuit safety.
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FAQ
Why must the LED forward voltage be below the supply?
The resistor drops the difference between them. With no difference there is nothing to drop and no operating point, so the calculation has no meaning.
What units should the current be in?
Milliamps or amps — the result is the same, and the unit is chosen next to the field.
Are inrush current and battery sag included?
No. The calculations are deterministic and use only the values you enter; discharge curves and start-up peaks are not modelled.
Is a standard resistor value suggested?
No, the calculator gives the exact computed resistance. Picking the nearest E12 or E24 value is left to you.
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