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DC POWER-SUPPLY SIZING TOOL
12V / 24V Power Supply Calculator
Convert load watts and amps, include startup demand and design headroom, and compare the current required from 12 V and 24 V DC supplies.
Watts or amps input
12 V and 24 V comparison
Peak factor and headroom
THE SAME POWER AT TWO VOLTAGES
P = V × I
12 V
Higher Current
More current for the same wattage
24 V
Lower Current
Half the current for the same wattage
Voltage compatibility must be confirmed from the motherboard or load documentation before selection.
INTERACTIVE CALCULATOR
Calculate the Required 12 V or 24 V Supply Rating
Enter the total continuous load as watts or measured current. The calculator applies the selected peak factor and design headroom without adding unrelated conversion losses.
LOAD AND SUPPLY INPUTS
Power-Supply Requirements
Supply Voltage
Select only a voltage supported by the connected equipment.
Enter Load As
W
Use the measured or datasheet maximum continuous load.
×
Use 1.00 when the entered load already represents the required peak.
%
Additional continuous rating above the calculated peak demand.
Do not double-count peak demand.
Set the peak factor to 1.00 when the entered wattage or current already includes startup and maximum operating conditions.
MINIMUM CONTINUOUS SUPPLY RATING
115.2 W
At least 9.60 A at 12 V
Continuous Load Power
80.0 W
Before peak factor and headroom
Continuous Load Current
6.67 A
At the selected 12 V supply
Peak Load Power
96.0 W
Continuous load × peak factor
Peak Load Current
8.00 A
At the selected 12 V supply
Minimum Current Rating
9.60 A
Includes selected design headroom
Example Next Supply Class
120 W
Use an available rating at or above the minimum
CURRENT COMPARISON
Same minimum wattage at 12 V and 24 V
12 V supply
9.60 A
24 V supply
4.80 A
Preliminary supply sizing complete
Confirm voltage compatibility, connector rating, cable drop, startup behavior, and thermal performance on the finished system.
This tool calculates steady-state DC output requirements. It does not certify inrush capability, cable ampacity, connector temperature rise, protection coordination, or regulatory compliance.
VOLTAGE COMPARISON
How 12 V and 24 V Change the Required Current
For the same power demand, doubling the supply voltage halves the current. The equipment must still explicitly support the selected input voltage.
Higher Current for the Same Power
At 120 W, a 12 V source supplies 10 A before cable and connector allowances.
120 W ÷ 12 V = 10 A
Lower Current for the Same Power
At 120 W, a 24 V source supplies 5 A, reducing current-dependent cable and connector stress.
120 W ÷ 24 V = 5 A
Voltage Is Not Interchangeable
A 24 V supply can damage equipment designed only for 12 V. Use the exact supported range shown in the board or system specification.
CALCULATION METHOD
Power, Current, Peak Demand, and Headroom Are Calculated Separately
The model preserves the physical relationship between volts, amps, and watts, then applies peak demand before the selected design headroom.
Power and Current
P = V × I
Use this relation to convert the entered watts or amps.
Peak Load
Ppeak = Pcontinuous × kpeak
The peak factor represents startup or maximum operating demand.
Minimum Supply Power
Pminimum = Ppeak × (1 + margin)
Headroom is applied after the peak load is established.
Minimum Supply Current
Iminimum = Pminimum ÷ V
The selected power supply must meet both watt and amp requirements.
INPUT GUIDANCE
Use Load Values That Match the Real Operating Condition
Calculator accuracy depends mainly on the load evidence entered. Use configured-system measurements whenever the hardware is available.
BEST INPUT
Measured Maximum Load
Measure the configured system during the real CPU, storage, accelerator, USB, display, and cooling workload.
GOOD PLANNING INPUT
Device Maximum Ratings
Add non-overlapping maximum values from the motherboard, storage, expansion, fan, and peripheral documentation.
EARLY DESIGN ONLY
Conservative Estimate
Document the assumptions, use a suitable peak factor and headroom, and replace estimates with measurements during validation.
| Input | Use This Value | Avoid This Error |
|---|---|---|
| Continuous load | Maximum sustained watts or measured current | Using idle power |
| Peak factor | Startup or maximum-to-continuous ratio | Applying a peak factor to an already-peak input |
| Headroom | Additional continuous output capacity | Treating headroom as a substitute for inrush testing |
| Supply voltage | Voltage explicitly supported by the load | Assuming 12 V and 24 V are interchangeable |
ENGINEERING SCOPE
What the Calculator Covers—and What Still Requires Validation
Use the result to shortlist a supply. Final approval still depends on the actual power source, wiring, connector, enclosure, workload, and environmental conditions.
Included in the Calculation
- Watts-to-amps and amps-to-watts conversion
- 12 V and 24 V current comparison
- User-defined peak or startup factor
- User-defined output-capacity headroom
- Minimum continuous watt and current ratings
Verify on the Finished System
- Millisecond-scale transient and inrush response
- Wire ampacity, cable voltage drop, and fuse selection
- Connector current rating and contact temperature rise
- Supply derating at ambient temperature and altitude
- Protection, grounding, EMI, and regulatory requirements
CONFIGURATION REVIEW
Need the Supply Checked Against a Real Mini-ITX Configuration?
Send the board model, CPU, storage, expansion devices, supply voltage, cable path, connector, and ambient-temperature requirements.FAQ
12 V and 24 V Power-Supply Sizing Questions
The FAQ uses native browser controls and remains usable even when page-level JavaScript optimization is delayed.
How do I calculate the amps required from a 12 V supply?
Divide the required DC output power in watts by 12 volts. For example, a 120 W load requires 10 A before any additional capacity margin.
How do I calculate the amps required from a 24 V supply?
Divide the required DC output power by 24 volts. A 120 W load requires 5 A at 24 V, which is half the current required at 12 V for the same power.
Can I replace a 12 V supply with a 24 V supply?
Only when the connected equipment explicitly supports 24 V input. Matching wattage does not make different voltages interchangeable, and excessive input voltage can damage the load.
What peak factor should I use?
Use a factor supported by measurement or device documentation. Enter 1.00 when the load value already represents the required peak; otherwise use a documented startup or maximum-to-continuous ratio.
Is 20% power-supply headroom always required?
No single margin fits every system. The appropriate value depends on load uncertainty, ambient derating, future expansion, supply characteristics, reliability targets, and the quality of the measured input data.
Does the result guarantee that the system will start?
No. Startup also depends on inrush current, transient response, protection thresholds, load sequencing, wiring impedance, and the actual behavior of the selected supply and connected hardware.