Enter both values to calculate watts
Volts (V)
Common:
Amps (A)
Watts (W)
Result will appear here
Understanding the Relationship
The relationship between watts, volts, and amps follows the Power Formula:
- Power (P) = Voltage (V) × Current (I)
- Voltage (V) = Power (P) ÷ Current (I)
- Current (I) = Power (P) ÷ Voltage (V)
In Solar Systems
Understanding these relationships helps you:
- Size your wiring - Higher amps need thicker wires
- Choose inverters - Match wattage to your needs
- Configure battery banks - 12V, 24V, or 48V systems affect current flow
- Calculate loads - Know how much power your devices draw
Real-World Solar Examples
Off-Grid Cabin Power Delivery
A 24V battery bank supplying 20A to an off-grid cabin delivers 480W. This tells you whether the system can support all connected loads.
Solar Panel STC Rating
A solar panel at 38.4V Vmp and 11.72A Imp produces 450W. This is exactly how Standard Test Condition wattage is derived — voltage and current at maximum power point define the panel's rated power.
Inverter AC Output
A 120V AC circuit from an inverter carrying 10A delivers 1,200W. This helps determine if the inverter is nearing its capacity limit.
When You'll Need This Conversion
- Sizing a Battery Bank for Known Loads — If your off-grid system runs at 48V and loads draw a peak of 40A, the battery bank must deliver at least 1,920W. This sets the minimum inverter size and informs battery capacity decisions.
- Evaluating Panel Performance at Different Temperatures — In cold weather, panel voltage rises. If Vmp shifts from 37V to 41V while current stays near 10A, power increases from 370W to 410W — explaining seasonal performance variation.
- Determining Power Through a Wire Run — If a wire carries 15A at 24V from charge controller to battery bank, 360W is being transmitted. Any voltage drop directly reduces delivered power.
Solar Tips & Common Mistakes
Voltage Drop Reduces Delivered Watts: If you lose 1.5V over a 30-foot run at 15A on a 24V circuit, you lose 22.5W — a 6.25% power loss. Keep voltage drop under 3% as recommended by NEC.
Higher Voltage Means Thinner Wires: A 1,200W load on a 12V system draws 100A (requiring very thick cable), but on a 48V system draws only 25A. This is why larger off-grid systems use 48V.
Panel Vmp ≠ System Voltage: A "12V nominal" solar panel has Vmp around 18V and Voc around 22V. The MPPT charge controller converts this higher panel voltage to battery voltage. Do not confuse panel voltage with battery system voltage.
Solar Calculators
Related Conversion Calculators
Last updated: January 3, 2026
