Home › Calculators

Electronics Calculators

Enter values and results update in real time. Worksheet figures are engineering estimates — validate critical designs before production.

Simplified / approximate models are marked. Precision depends on component tolerances and measurement conditions.

Available calculators

Ohm's Law (V = I × R)

Enter any two of Voltage (V), Current (I) and Resistance (R); power is computed from the filled values.

Voltage (V)

Current (I)

Resistance (R)

Voltage V = I × R

—

Current I = V / R

—

Resistance R = V / I

—

Power P

—

Fill any two fields. Leave the target empty.

Voltage Divider

V_out = V_in × R2 / (R1 + R2). Unloaded divider.

Input voltage Vin

Series resistance R1

Shunt resistance R2

Output voltage Vout

—

Ignores load current. A significant load on Vout reduces the real value.

LED Series Resistor

Resistor value to set LED current: R = (Vs − Vf) / I.

Supply voltage Vs

LED forward voltage Vf

Target current I

Exact resistance

—

Nearest E24 resistance

—

Resistor power

—

Nearest preferred value in the E24 series. TYP: red ~1.8–2.0 V, white/blue ~2.8–3.3 V, IR ~1.2 V.

RC Time Constant & Cutoff

τ = R × C; low-pass cutoff f = 1 / (2πRC).

Resistance R

Capacitance C

Time constant τ

—

Cutoff frequency fc

—

For a 4.7 kΩ / 100 nF pair: τ ≈ 0.47 ms, fc ≈ 339 Hz.

LC Resonant Frequency

f₀ = 1 / (2π√(LC)).

Inductance L

Capacitance C

Resonant frequency f₀

—

Op-Amp Gain (Ideal)

Ideal infinite-gain model; gain set by feedback resistors only.

Amplifier type

Feedback resistor Rf

Input resistor Rg

Gain (ideal)

—

Gain = 1 + Rf/Rg

Real op-amps are limited by gain-bandwidth product and supply rails.

Power ↔ dBm

Convert between linear power (W / mW) and dBm (reference 1 mW).

Power (mW)

Power (dBm)

dBm

Power in dBm

—

Power in mW

—

dBm = 10·log10(P[mW]) · P[mW] = 10^(dBm/10)

Series & Parallel Resistors

Equivalent resistance of two resistors in series and in parallel.

Resistor R1

Resistor R2

Series R = R1 + R2

—

Parallel R = (R1·R2)/(R1+R2)

—

n identical resistors in parallel → R/n; in series → n·R.

555 Astable (Oscillator)

Free-running square wave. f = 1.44 / ((RA + 2·RB)·C).

Resistor RA

Resistor RB

Capacitor C

Frequency f

—

Duty cycle

—

High time (charge)

—

Low time (discharge)

—

Ideal model. Keep RA ≥ 1 kΩ, RB ≥ 1 kΩ; real tolerances shift timing.

555 Monostable (One-shot)

Output pulse width after a trigger: T = 1.1·R·C.

Resistor R

Capacitor C

Pulse width T

—

LM317 Output Voltage

Vout = Vref·(1 + R2/R1), Vref = 1.25 V (Iadj·R2 usually negligible).

Output voltage Vout

—

Iadj·R2 (~50 µA·R2) adds a few mV; typical R2/R1 ≤ 10 for stability. Mind dropout (~2 V) and minimum load.

Battery Runtime

Approximate runtime from capacity and average current: h = Capacity / I.

Battery capacity

Average current

Runtime

—

Rough estimate. Real runtime is lower due to conversion losses, self-discharge, ESR, SoC limits and temperature.

NTC Thermistor (Beta)

Temperature from measured resistance (Beta equation): 1/T = 1/T0 + (1/B)·ln(R/R0).

Resistance @25°C (R0)

Beta (B)

Measured resistance R

Temperature

—

Beta is a two-parameter approximation over a limited range. A common probe is 10 kΩ with B≈3435. Wire and contact resistance add error.