DC Power Calculator – P = V × I
Enter any two values below (Voltage, Current, Resistance, Power) and click Calculate. The other two are solved automatically.
How DC Power Relates to V, I, and R
Electrical power in a DC circuit is the rate that electrical energy is converted into another form (like heat or light). The core identities are:
- \( P = V I \) (power equals voltage times current)
- \( V = I R \) (Ohm’s law)
- Combining them: \( P = I^2 R \) and \( P = \frac{V^2}{R} \)
If you know any two of \(V\), \(I\), \(R\), and \(P\), you can compute the others. For example, if you have a \(12\ \text{V}\) battery and a \(48\ \Omega\) resistor: \( I = V/R = 12/48 = 0.25\ \text{A} \) and \( P = VI = 12 \times 0.25 = 3\ \text{W} \).
Tip: Keep units consistent (V, A, Ω, W). This tool auto-scales outputs to readable units (e.g., mA, kΩ, mW).
Frequently Asked Questions
Can I enter milli/mega units?
Yes — use the unit dropdowns (mV, mA, kΩ, MΩ, mW, kW). The calculator converts to SI units internally.
Does this work for AC?
No — this page assumes steady DC. For alternating current, see the AC Power Calculator which handles power factor.
Is everything private?
Yes. All calculations run in your browser; no data is uploaded.
Understanding DC Power
In a direct current (DC) circuit, electric charge flows in one constant direction. This is different from alternating current (AC), where the flow reverses direction periodically. Common sources of DC include batteries, solar panels, and USB power supplies.
Basic Power Formula
The relationship between voltage, current, and power is straightforward in DC:
$$ P = V \times I $$
- P = Power (watts, W)
- V = Voltage (volts, V)
- I = Current (amperes, A)
For example, a 12-volt battery powering a 2-amp device consumes:
$$ P = 12 \times 2 = 24 \,\text{W} $$
Ohm’s Law Connection
Ohm’s Law links voltage, current, and resistance:
$$ V = I \times R $$
By combining this with the power formula, we get additional forms:
- $$ P = I^2 \times R $$
- $$ P = \frac{V^2}{R} $$
This makes it possible to calculate power even if you only know voltage and resistance, or current and resistance.
Units and Practical Use
Power is measured in watts (W). Larger devices may use kilowatts (kW), while small electronics often use milliwatts (mW). For students and hobbyists, knowing how to calculate DC power is essential for sizing batteries, resistors, and power supplies.
Tip: Always double-check your units! Mixing volts, milliamps, and ohms without converting to standard units can lead to wrong answers.