Complex Number & Phasor Calculator

Convert rectangular ↔ polar form, and add, subtract, multiply or divide complex numbers/phasors.
Rectangular ↔ Polar
Add / Subtract
Multiply / Divide

Rectangular ↔ Polar Conversion

r = √(a²+b²)  •  θ = atan2(b,a)   |   a = r·cosθ, b = r·sinθ
3+4i
10∠30°
Enter values and press Calculate.

Phasor Diagram (live)

Add / Subtract Two Complex Numbers

(a1+b1i) ± (a2+b2i) = (a1±a2) + (b1±b2)i
(3+4i) & (1−2i)
Enter values and press Calculate.

Phasor Diagram: Z1, Z2, Sum (live)

Multiply / Divide Two Complex Numbers

Z1×Z2: r1r2∠(θ12)  •  Z1/Z2: (r1/r2)∠(θ1−θ2)
(3+4i) & (1−2i)
Enter values and press Calculate.

Why AC Circuit Analysis Uses Complex Numbers

In an AC circuit, voltage and current are not just magnitudes — they also have a phase relative to each other, caused by inductors and capacitors. Representing a sinusoidal signal as a phasor (a complex number) captures both magnitude and phase in one compact quantity, letting engineers use simple algebra (instead of calculus/trigonometric identities) to add, subtract, multiply and divide AC quantities like impedance, voltage, and current.

Rectangular vs polar form

OperationBest formRule
Addition/subtractionRectangularAdd/subtract real and imaginary parts separately
MultiplicationPolarMultiply magnitudes, add angles
DivisionPolarDivide magnitudes, subtract angles
Rectangular→Polarr=√(a²+b²), θ=atan2(b,a)
Polar→Rectangulara=r·cosθ, b=r·sinθ

Real-World Applications & Fully-Explained Examples

Worked examples — explained in full

1. Converting 3+4i to polar form. r=√(3²+4²)=√25=5. θ=atan2(4,3)≈53.13°. So 3+4i = 5∠53.13°.
2. Converting 10∠30° to rectangular form. a=10×cos(30°)=10×0.866≈8.660. b=10×sin(30°)=10×0.5=5.000. So 10∠30° = 8.660+5.000i.
3. Adding (3+4i)+(1−2i). Real: 3+1=4. Imaginary: 4+(−2)=2. Result: 4+2i — simple component-wise addition, exactly like combining two series impedances.
4. Multiplying (3+4i)×(1−2i). Using FOIL: (3×1)+(3×−2i)+(4i×1)+(4i×−2i)=3−6i+4i−8i². Since i²=−1: 3−6i+4i+8=11−2i.
5. Dividing (3+4i)/(1−2i) using the polar method. 3+4i=5∠53.13°, 1−2i=2.236∠−63.43°. Quotient: (5/2.236)∠(53.13−(−63.43))=2.236∠116.57°, converting back to rectangular: −1+2i — confirmed by direct algebraic division (multiplying by the conjugate) giving the identical result.
6. Why polar form is easier for division. Doing example 5's division directly in rectangular form requires multiplying by the complex conjugate of the denominator (1+2i) and simplifying — several algebra steps. In polar form it's just one division and one subtraction (magnitudes and angles), which is exactly why AC impedance/admittance problems are almost always solved by switching to polar form for multiplication and division steps.

Frequently Asked Questions

How do I convert a complex number to polar form?

r=√(a²+b²) for the magnitude, and θ=atan2(b,a) for the angle (using the two-argument arctangent to get the correct quadrant). For example, 3+4i becomes 5∠53.13°.

How do I convert a phasor from polar back to rectangular form?

a=r×cos(θ) for the real part, and b=r×sin(θ) for the imaginary part. For example, 10∠30° becomes 8.66+5i.

Why is rectangular form better for addition and polar form better for multiplication?

Adding complex numbers in rectangular form is just adding the real and imaginary parts separately — simple and direct. Multiplying in rectangular form requires FOIL expansion and simplifying i²=-1, which gets messy; polar form reduces multiplication to just multiplying magnitudes and adding angles, which is far simpler.

What is a phasor in AC circuit analysis?

A phasor is a complex number representing a sinusoidal signal's magnitude and phase angle at a single frequency, letting you use algebra instead of calculus/trigonometry to analyze AC circuits — voltage, current, and impedance are all commonly represented as phasors.

How do I add two impedances in series?

Add them in rectangular form: Z_total = (R1+R2) + (X1+X2)i, where R is resistance and X is reactance (positive for inductive, negative for capacitive).

How do I combine impedance for parallel components?

Convert both impedances to polar form, then use Z_parallel = (Z1×Z2)/(Z1+Z2) — the multiplication is easy in polar form, but the addition in the denominator still needs rectangular form, so parallel impedance combination typically requires converting back and forth between forms.

What does the angle of a phasor represent physically?

It represents the phase shift of that sinusoidal quantity relative to a reference (often the source voltage) — a positive angle means the quantity leads the reference in time, and a negative angle means it lags.

Why does dividing by i give a -90° phase shift?

Since i = 1∠90°, dividing by i is equivalent to subtracting 90° from the angle (per the polar division rule), which is exactly the -90° phase shift seen in capacitive reactance calculations (Xc = 1/(jωC) = -j/(ωC)).

How is this different from a simple scientific calculator's complex number mode?

It isn't fundamentally different mathematically — this calculator is specifically designed around the rectangular/polar workflow and terminology used in AC circuit analysis (phasors, impedance), with a live phasor diagram to visualize the result, which general scientific calculators typically don't provide.

Can I use this for three-phase power calculations?

Yes — three-phase quantities are commonly represented as phasors 120° apart, and this calculator's add/subtract and multiply/divide operations directly support the phasor arithmetic used in unbalanced three-phase analysis and symmetrical components.

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