The complete set of electronics calculators that started it all — Ohm's law, reactance, resonance, decibels, color codes and more. Every tool shows its formula and the worked steps, so you learn the math while you solve. Pick one below to begin.
Ohm's Law
V = I × R · Enter any two values to calculate the third.
Solve for Voltage, Current, or Resistance
V = I × R | I = V / R | R = V / I
V
A
Ω
Tip: The Ohm's Law triangle (V on top, I × R on bottom) lets you cover the unknown and read the formula. Memorise it — it appears in almost every DC circuit question.
Electrical Power
P = V × I = I² × R = V² / R · Enter any two values.
Power Calculator
P = V×I = I²R = V²/R
W
V
A
Ω
Tip: Power in watts = energy per second (joules/second). For resistors, higher resistance at same current means more heat (P = I²R).
Resistor Combinations
Series: R = R1+R2+… · Parallel: 1/R = 1/R1+1/R2+…
Series Resistors
R_total = R1 + R2 + R3 + …
Ω
Parallel Resistors
1/R = 1/R1 + 1/R2 + 1/R3 + …
Ω
Two Resistors in Parallel (quick)
R = (R1 × R2) / (R1 + R2)
Ω
Ω
Tip: Two equal resistors in parallel = half one resistor's value. Parallel total is always less than the smallest resistor.
Voltage Divider
Vout = Vin × R2 / (R1 + R2)
Unloaded Voltage Divider
Vout = Vin × R2 / (R1 + R2)
V
Ω
Ω
Current Divider
I1 = Itotal × R2 / (R1 + R2)
A
Ω
Ω
Battery Internal Resistance
Vout = EMF − (Rint × Iout)
Terminal Voltage
Vout = EMF - (Rint × Iout)
V
Ω
A
Find Internal Resistance
Rint = (EMF - Vload) / I
V
V
A
Tip: A battery's terminal voltage drops under load due to internal resistance. A good battery has very low Rint — often less than 1Ω.
Kirchhoff's Laws
KVL: sum of voltages around any loop = 0 · KCL: sum of currents at any node = 0
KVL — Find unknown voltage
V1 + V2 + V3 + … + Vx = Vsource
V
V
KCL — Find unknown current
I_in = I_out1 + I_out2 + … + I_x
A
A
Tip: KVL and KCL are the foundation of all circuit analysis. In a series circuit, all voltages add to the source. In a parallel circuit, all branch currents add to the total.
Sine Wave Conversions
Convert between Peak, RMS (effective), and Average values.
From Peak Value
RMS = 0.707 × Vpeak · Avg = 0.637 × Vpeak
V
From RMS Value
Vpeak = 1.414 × RMS · Avg = 0.9 × RMS
V
Peak-to-Peak
Vpp = 2 × Vpeak
V
Period ↔ Frequency
f = 1 / T · T = 1 / f
Tip: US mains power is 120V RMS. Peak = 120 × 1.414 = 169.7V. The "120V" you see on appliances is the RMS (effective) value.
Reactance — XL & XC
XL = 2πfL · XC = 1 / (2πfC)
Inductive Reactance (XL)
XL = 2π × f × L
Capacitive Reactance (XC)
XC = 1 / (2π × f × C)
Tip: XL increases with frequency; XC decreases with frequency. At resonance, XL = XC.
Impedance (Z)
Series: Z = √(R² + (XL−XC)²) · Parallel: Z = RX / √(R²+X²)
Tip: After 1τ a capacitor is 63.2% charged; after 5τ it's 99.3% — considered fully charged. This rule applies to both RC and RL circuits.
AC Power & Power Factor
True Power (W) = Apparent Power (VA) × Power Factor
True / Apparent / Reactive Power
P = S × PF · Q = √(S²−P²)
V
A
°
Find Power Factor
PF = cos(θ) = P / S
W
VA
Tip: PF = 1 means purely resistive (all power is true power). PF = 0 means purely reactive (no real work done). Motors and transformers have PF < 1.
Capacitors
Parallel: C = C1+C2+… · Series: 1/C = 1/C1+1/C2+…
Capacitors in Parallel
C_total = C1 + C2 + C3 + …
μF
Capacitors in Series
1/C = 1/C1 + 1/C2 + …
μF
Tip: Capacitors combine opposite to resistors — parallel adds, series reciprocals. Voltage rating in series divides proportionally.
Inductors
Series: L = L1+L2+… · Parallel: 1/L = 1/L1+1/L2+…
Inductors in Series
L_total = L1 + L2 + L3 + …
mH
Inductors in Parallel
1/L = 1/L1 + 1/L2 + …
mH
Inductor Energy
W = ½ × L × I²
A
Tip: Inductors (like resistors) add in series, and use reciprocals in parallel — opposite to capacitors. No mutual coupling assumed here.
Transformer Ratios
Vp/Vs = Np/Ns · Ip/Is = Ns/Np · Zp/Zs = (Np/Ns)²
Turns & Voltage
Vp / Vs = Np / Ns
turns
turns
V
Current & Impedance
Ip / Is = Ns / Np · Zp / Zs = (Np/Ns)²
A
Ω
Tip: Enter the two turns counts (required); voltage, current, and load are optional and fill in whatever you provide. Step-up transformer: voltage rises but current falls by the same factor — power is conserved.
Resistor Color Code
Decode 4-band and 5-band resistors using the standard EIA resistor color code.
4-Band Resistor Decoder
Value = (10×D1 + D2) × Multiplier
5-Band Resistor Decoder
Value = (100×D1 + 10×D2 + D3) × Multiplier
Reference Table
Color
Digit
Multiplier
Tolerance
Tip: Mnemonic — "Bad Boys Ravage Our Young Girls But Violet Gives Willingly": Black Brown Red Orange Yellow Green Blue Violet Gray White.
Capacitor Codes & Conversions
Decode 3-digit ceramic/film capacitor codes and convert between units.
3-Digit Capacitor Code
Value(pF) = AB × 10^C
Unit Converter
1 F = 10⁶ μF = 10⁹ nF = 10¹² pF
Frequency & Wavelength
c = f × λ where c = 3×10⁸ m/s (speed of light)
Frequency ↔ Wavelength
λ(m) = 3×10⁸ / f(Hz) · f = 3×10⁸ / λ
Hz
m
Antenna Length
Half-wave = λ/2 · Quarter-wave = λ/4
Period ↔ Frequency
T = 1/f · f = 1/T
Hz
s
Tip: FM radio (88–108 MHz) → wavelength ≈ 2.8–3.4 m. AM radio (540–1700 kHz) → wavelength ≈ 176–556 m. Higher frequency = shorter wavelength.
Decibels (dB)
Voltage gain: 20log(Vout/Vin) · Power gain: 10log(P2/P1)
Voltage Gain in dB
dB = 20 × log₁₀(Vout / Vin)
V
V
Power Ratio in dB
dB = 10 × log₁₀(P2 / P1)
W
W
dB → Voltage Ratio
Vout/Vin = 10^(dB/20)
dB
Tip: Key dB values to memorise — +3dB = ×2 power (×1.414 voltage); +6dB = ×4 power (×2 voltage); +20dB = ×100 power (×10 voltage); −3dB = half power (−3dB point of a filter).
Op-Amp Gain
Inverting: Av = −Rf/Ri · Non-inverting: Av = 1 + Rf/Ri
Inverting Amplifier
Av = −(Rf / Ri)
Ω
Ω
V
Non-Inverting Amplifier
Av = 1 + (Rf / Ri)
Ω
Ω
V
Voltage Follower (Buffer)
Av = 1 · Vout = Vin
V
Tip: Inverting amp has 180° phase shift (output is inverted). Non-inverting has no phase shift. Both have virtual ground at the inverting input when in negative feedback.
RC / RL Filters
Cutoff frequency (−3dB point): fc = 1/(2πRC) or fc = R/(2πL)
RC Filter Cutoff Frequency
fc = 1 / (2π × R × C)
RL Filter Cutoff Frequency
fc = R / (2π × L)
Tip: Below fc = low-pass passes signal; above fc = high-pass passes signal. At fc the output is 3dB down (70.7% of input voltage).
SI Prefixes & Unit Converter
Convert between pico, nano, micro, milli, kilo, mega, giga, tera.
Unit Converter
Enter value and convert between SI prefixes
SI Prefix Table (from formula reference)
Prefix
Symbol
Multiplier
Power of 10
tera
T
trillion
10¹²
giga
G
billion
10⁹
mega
M
million
10⁶
kilo
k
thousand
10³
—
—
one
10⁰
milli
m
1/thousandth
10⁻³
micro
μ
1/millionth
10⁻⁶
nano
n
1/billionth
10⁻⁹
pico
p
1/trillionth
10⁻¹²
Algebra Solver
Solve linear and quadratic equations step by step.
Equation Solver
Linear: ax + b = c · Quadratic: ax² + bx + c = 0
Trigonometry
sin, cos, tan — exact values and inverse calculations.
Evaluate sin / cos / tan
Enter angle in degrees
°
Inverse trig (find angle)
arcsin / arccos / arctan
Common Exact Values
Angle
sin
cos
tan
0°
0
1
0
30°
1/2
√3/2
1/√3
45°
√2/2
√2/2
1
60°
√3/2
1/2
√3
90°
1
0
undefined
Statistics
Mean, median, mode, range, standard deviation.
Data Set Analysis
Enter numbers separated by spaces
Fractions
Add, subtract, multiply, divide fractions with full working.