Electrical Calculator Hub
Solve Ohm’s law, power, energy cost, voltage drop, and basic wire sizing in one place. Ideal for students, hobbyists, and quick field checks.
Ohm’s Law Calculator
Enter any two values and the calculator will solve the remaining two.
Key electrical formulas used in this hub
These calculators rely on a small set of core relationships that appear again and again in electrical engineering and practical wiring.
Ohm’s law
Ohm’s law: \( V = I \cdot R \)
- \(V\) = voltage (volts, V)
- \(I\) = current (amperes, A)
- \(R\) = resistance (ohms, Ω)
From this we can derive:
- \( I = \dfrac{V}{R} \)
- \( R = \dfrac{V}{I} \)
Electrical power and energy
Instantaneous power:
- \( P = V \cdot I \)
- Using Ohm’s law: \( P = I^2 R = \dfrac{V^2}{R} \)
Energy consumption:
- \( E_{\text{kWh}} = \dfrac{P_{\text{W}}}{1000} \cdot t_{\text{hours}} \)
- Cost = \( E_{\text{kWh}} \times \text{tariff} \)
Series and parallel resistance
Series: resistances add directly
\( R_{\text{eq}} = R_1 + R_2 + \dots + R_n \)
Parallel: conductances add
\( \dfrac{1}{R_{\text{eq}}} = \dfrac{1}{R_1} + \dfrac{1}{R_2} + \dots + \dfrac{1}{R_n} \)
Voltage drop in a copper conductor (DC)
For a two-conductor run (out and back) of length \(L\) (one-way) with cross-sectional area \(A\) and current \(I\):
\( R = \rho \dfrac{2L}{A} \)
\( \Delta V = I \cdot R \)
where \(\rho\) is the resistivity of copper (≈ \(1.72 \times 10^{-8}\ \Omega\cdot\text{m}\)).
Quick wire size estimation logic
The wire-size suggestion tool in this hub:
- Computes the maximum allowable resistance from your voltage-drop limit.
- Back-calculates the minimum cross-sectional area needed for that resistance.
- Checks that the current is within a simple ampacity heuristic for each common size.
This is intentionally conservative but still only an approximation. For real projects, always consult official tables (NEC, IEC, BS 7671, etc.) and a qualified professional.
Safety notes and limitations
- This tool is for education and quick estimates, not for final design.
- It does not account for temperature, bundling, insulation type, or installation method.
- AC systems with power factor, harmonics, or three-phase arrangements require more advanced calculations.
- Before modifying any fixed wiring, follow local regulations and, where required, hire a licensed electrician.
Frequently asked questions
Can I use this for household wiring design?
No. You can use it to build intuition and sanity-check numbers, but household wiring must follow your local electrical code and be inspected where required.
Does it support three-phase power?
This page focuses on single-phase and DC basics. For three-phase power and more advanced topics, use the dedicated engineering calculators on CalcDomain (for example, the three-phase power and NEC ampacity tools).
Why do I sometimes get an error instead of a result?
The calculator checks for inconsistent or insufficient inputs (for example, only one Ohm’s-law value, or negative resistance). When that happens, it shows a short error message instead of guessing.