USB-C can be spicy
USB Power Delivery goes up to 48 V at 5 A (240 W). That’s enough to run a gaming laptop—over the same port that once carried 2.5 W.
Tiny connector, big watts
DC Power Calculator — P = V × I
Inputs
Use DC values.
Amperes or milliamps.
Ohms, kiloohms, or megaohms.
Watts, milliwatts, or kilowatts.
Results
Results will appear here.
Tip: Enter exactly two values; leave the other two blank.
DC Power Calculator: quick, clear electrical estimates
This DC power calculator helps you find the relationship between voltage, current, resistance, and power in a direct current circuit. It’s ideal for students, DIY electronics, and anyone sizing a battery, resistor, or power supply. Enter any two values, and the calculator solves for the others so you can understand how much power a circuit will draw or deliver.
DC power in plain language
Direct current (DC) means electricity flows in one steady direction, like in batteries, solar panels, and USB chargers. Voltage is the electrical “push,” current is how much charge is moving, and resistance is how much the circuit resists that flow. Power is the rate of energy use and is measured in watts. In simple DC circuits, these values are tied together by two core relationships: the power equation and Ohm’s law.
Key formulas the calculator uses
The basic DC power formula is:
$$ P = V \times I $$
And Ohm’s law links current, voltage, and resistance:
$$ V = I \times R $$
Combining them gives two additional power forms:
- $$ P = I^2 \times R $$
- $$ P = \frac{V^2}{R} $$
That means you can calculate power from voltage and resistance, or from current and resistance, even when you don’t know all four values.
How to use the calculator
- Enter any two values (voltage, current, resistance, or power).
- Pick the correct units, such as volts, amps, ohms, and watts (or milli/kilo/mega variants).
- Click Calculate to solve for the missing values.
- Review the results and confirm they match your real-world setup.
Real-world examples
- Battery sizing: Estimate how much power a 12 V system draws at 2 A (24 W).
- LED circuits: Choose a resistor that limits current while keeping power safe.
- USB devices: Check whether a 5 V, 2 A charger can power your gadget.
- Solar projects: Convert panel voltage and current into watts to compare outputs.
Units and practical tips
Power is measured in watts (W), while small electronics may use milliwatts (mW) and larger loads use kilowatts (kW). Current is in amps (A), voltage in volts (V), and resistance in ohms (Ω). If you input milliamps or kilohms, the calculator converts everything to standard units internally.
Tip: Always double-check units. Mixing volts with milliamps or ohms without converting can lead to incorrect results.
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 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.
5 Fun Facts about DC Power
Phones sip in pulses
Many phone chargers use rapid DC pulses to push charge, then taper off. Your “5 V” label hides a fast dance between voltage, current, and heat.
Charging choreography
Wiring losses are I²R
Double the current and you quadruple resistive heating. That’s why higher-voltage DC (like 24 V instead of 12 V) keeps cables cooler at the same power.
Heat math
LEDs set their own volts
LEDs drop a nearly fixed voltage (e.g., ~2 V red, ~3 V blue). What saves them is current limiting—the reason resistors matter in “simple” DC circuits.
Current is king
Solar panels are current sources
PV panels happily sit near a fixed current until voltage rises to their max power point. Shade one cell, and the panel’s current collapses unless bypass diodes step in.
Sun math