DC kW Calculator
Direct-current power calculator for solar, batteries, and EV systems. Simple V × A formula with no power factor.
Common conversions
| Input | Result |
|---|---|
| 12 V @ 10 A (car accessory) | 0.12 kW |
| 24 V @ 50 A (golf cart/telecom) | 1.2 kW |
| 48 V @ 100 A (battery bank) | 4.8 kW |
| 400 V @ 15 A (solar string) | 6.0 kW |
| 380 V @ 25 A (telecom DC bus) | 9.5 kW |
| 800 V @ 200 A (EV fast charging) | 160.0 kW |
The math behind it
- kW = (600 × 250) / 1000
- kW = 150,000 / 1000
- kW = 150 kW
Everything you need to know
DC power is the simplest power calculation in electrical work: multiply volts by amps and divide by 1000. Unlike AC, there's no power factor term because direct current never alternates, so voltage and current stay in phase by definition. Every watt calculated this way is real, usable power.
Where DC power calculations show up
- Batteries and battery banks: pack voltage times discharge current gives the instantaneous kW available to an inverter or DC load, and checking that against the pack's C-rate limit shows what it can actually sustain.
- Solar arrays (DC side): string voltage times current at maximum power point (Vmp x Imp) gives the array's DC kW before inverter losses, the figure that has to stay inside the inverter's DC input window.
- EV traction systems: battery pack voltage times motor phase current approximates instantaneous propulsion power, which is how manufacturers back-check the kW figures behind a 0-60 time.
- Telecom DC plants: most central offices and cell sites run on -48 V DC distribution, where rectifiers convert AC mains to DC and this same formula sizes the DC bus and battery backup.
Why DC has no power factor
Power factor exists because AC voltage and current can shift out of phase when a circuit has inductance or capacitance, so some of the apparent power moves back and forth without doing work. DC voltage and current don't oscillate, so there's no phase angle to shift and no reactive component to strip out. The one exception worth knowing: switch-mode power supplies and some DC-DC converters produce ripple, a small AC component riding on the DC output. For a typical battery or solar circuit, ignore it; for a supply with meaningful ripple, use the RMS current value in the formula instead of the average.
Use the voltage you actually measure, not the nominal rating
A battery's terminal voltage moves with state of charge, often by 15% to 20% between full and empty. A "48 V" lithium pack might sit at 54 V fully charged and sag to 44 V near empty, so the same 100 A draw represents anywhere from 4.4 kW to 5.4 kW depending on charge state. Use the voltage from a meter or BMS reading at the moment that matters, not the nominal label on the pack, whenever the calculation needs to be accurate rather than approximate.
Common applications
Multiply pack voltage by max continuous current to get usable kW for inverter loading and BMS limits.
String voltage times Imp gives the array's DC kW at MPP. Match against the inverter's MPPT window and current limits.
Pack V x motor current equals instantaneous propulsion kW, used to verify performance against published 0-60 specs.
Central offices and many data centers distribute -48 V DC from rectifiers to avoid a single AC failure point. The same V × A / 1000 formula sizes the DC bus and battery-backup runtime.
Common mistakes
Battery voltage varies 15% to 20% from full to empty. Use the actual state-of-charge voltage for accurate kW at any moment.
An EV charger's AC draw from the grid is higher than the DC power delivered to the battery because of rectifier and cooling losses. Don't use the AC nameplate rating to estimate DC charging speed.
DC circuits carrying high current over long cable runs (solar combiner to inverter, battery to bus bar) can lose several percent of kW to cable resistance. Check voltage drop separately; this calculator assumes the voltage entered is measured at the load.
A 100 Ah pack with a 1C limit can't sustainably supply much more than 100 A no matter what the kW math says. Check the cell or pack C-rate before assuming the calculated current is achievable.
Frequently asked questions
What about ripple?+
Ignore it for typical battery DC. For switch-mode power supply outputs with meaningful ripple, use the RMS current instead of the average current in the formula.
Does DC power have a power factor?+
No. Power factor only applies where voltage and current can shift out of phase, which requires an alternating waveform. DC current and voltage don't alternate, so every watt calculated is real power.
How many kW is a 48 V battery bank drawing 100 A?+
4.8 kW (48 × 100 / 1000), assuming the pack is actually sitting at 48 V rather than its nominal rating.
Why do EV fast chargers list different AC and DC kW figures?+
Because the AC input includes conversion losses. A charger might draw 160 kW of AC from the grid but only deliver about 150 kW of DC to the battery after rectifier and cooling losses.
Is DC kW the same as AC kW for the same volts and amps?+
No. AC real power equals volts x amps x power factor, so anything below PF 1.0 delivers less real power than the same DC voltage and current.
How much power does a solar string produce at its maximum power point?+
String Vmp × Imp, divided by 1000. A string at 400 V and 15 A produces about 6 kW DC, before inverter conversion losses.
Should I use nominal or measured voltage for a battery kW calculation?+
Use the measured voltage. A nominal 48 V pack can swing from about 44 V to 54 V across its charge range, changing the calculated kW by more than 20% for the same current.
Why do telecom sites run on -48 V DC?+
For battery backup and safety margin. -48 V DC survives a rectifier failure on battery alone, and it falls below the voltage threshold considered hazardous to touch, unlike the higher DC bus voltages used in EVs and solar.
Does this formula work for calculating EV traction power?+
Yes, as an approximation. Pack voltage times motor phase current gives instantaneous propulsion power, though real drivetrains add inverter losses that trim a few percent off the mechanical result.
Do I need to know the load type to use this DC formula?+
No. The V × A / 1000 formula holds for any DC load, resistive or not, because there's no phase angle or reactive component to account for.