Electrical Calculator Guide
An electrical calculator solves relationships among voltage (V), current (I), resistance (R), and power (P) using Ohm's law and power identities. It also handles series/parallel combinations and basic AC power with power factor (pf).
What is Electrical Calculator?
The electrical calculator is for students, technicians, and hobbyists. Enter any two of V, I, R, P to solve the rest, compute series/parallel equivalents, and estimate AC real power with pf.
How to Use the Electrical Calculator
- Choose a mode: Ohm's law, power, series/parallel, or AC power.
- Enter known values with units (V, A, ohm, W).
- Calculate unknowns; convert units (mA, kohm, kW) as needed.
- Refine with tolerance/derating for real parts.
- Document results for your build or lab report.
Formulas & Methods
- Ohm's law:
V = I*R,I = V/R,R = V/I - Power (resistive):
P = V*I = I^2*R = V^2/R - Series:
R_T = sum R_i - Parallel:
1/R_T = sum (1/R_i)(two-resistor shortcutR_T = R1*R2/(R1+R2)) - AC power:
S = V_rms*I_rms(VA),P = S*pf(W),Q = S*sin(phi)(var), withpf = cos(phi).
Assumptions & limitations
- Power identities assume resistive loads; reactive elements need complex impedance.
- AC formulas use rms values and a single frequency.
- Real components have tolerance and temperature coefficients.
Examples
Example A — Ohm's law
V=12 V, R=220 ohm -> I = 12/220 ~ 54.5 mA; P = V*I ~ 0.654 W (use >=1 W resistor).
Example B — AC power with pf
V_rms=120 V, I_rms=5 A, pf=0.8 -> P = 120*5*0.8 = 480 W.
| Task | Formula | Result |
|---|---|---:|
| Parallel 1 kohm || 1 kohm | R_T = 500 ohm |
| Series 100 ohm + 330 ohm | sum R | 430 ohm |
Pro Tips & Best Practices
- Measure twice—verify assumptions with a multimeter before energizing.
- Derate parts: use resistors >=2x expected dissipation for reliability.
- For AC motors/SMPS, consider inrush and pf correction.
- Use fuses or current-limited supplies during prototyping.
Related Calculators
FAQ
Q: What does Ohm's law state?
A: Voltage (V) = Current (I) * Resistance (R). It is the foundation for DC circuit calculations.
Q: How do I calculate power?
A: P = V * I = I^2 * R = V^2 / R for resistive loads.
Q: Series vs parallel—what changes?
A: Series adds resistances; parallel adds conductances. Voltage and current divide differently in each.
Q: What about AC and power factor?
A: For AC, apparent power S = V_rms * I_rms; real power P = S * pf; reactive power Q = S * sin phi.
Q: Safety tips?
A: De-energize circuits, verify with a meter, and respect voltage/current ratings.
Engineering note: SI units assumed; AC examples use single-phase rms values at fixed frequency.
Call to Action
Enter any two of V, I, R, and P to solve your circuit quickly—then size components with a safety margin before you build.