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Power Supply Calculator

Size your PSU from component power draw

Recommended PSU

550 W

DC Load

423 W

AC Draw

635 W

Recommended PSU

550 W

DC Load

423 W

With Headroom

508 W

AC Draw

635 W

Rails

2

Power by Rail

12V rail420.0 W
3.3V rail3.3 W

What You'll Need

HUANCHAIN 50 FT 12/3 Gauge Heavy Duty Outdoor Extension Cord Waterproof with Lighted end, Flexible Cold-Resistant 3 Prong Electric Cord Outside, 15Amp 1875W 12AWG SJTW, Yellow, ETL

HUANCHAIN 50 FT 12/3 Gauge Heavy Duty Outdoor Extension Cord Waterproof with Lighted end, Flexible Cold-Resistant 3 Prong Electric Cord Outside, 15Amp 1875W 12AWG SJTW, Yellow, ETL

$41.994.8
View on Amazon
Surge Protector Power Strip - HANYCONY 8 Outlets 4 USB (2 USB C) Charging Ports, Multi Plug Outlet Extender, 5Ft Braided Extension Cord, Flat Plug Wall Mount Desk Charging Station for Home Office ETL

Surge Protector Power Strip - HANYCONY 8 Outlets 4 USB (2 USB C) Charging Ports, Multi Plug Outlet Extender, 5Ft Braided Extension Cord, Flat Plug Wall Mount Desk Charging Station for Home Office ETL

$9.994.8
View on Amazon
Jackery Explorer 500 v2 Portable Power Station, 512Wh LiFePO4 Battery, 500W AC/1000W Peak, Solar Generator for Camping, Outdoors, and Power Outages

Jackery Explorer 500 v2 Portable Power Station, 512Wh LiFePO4 Battery, 500W AC/1000W Peak, Solar Generator for Camping, Outdoors, and Power Outages

$339.004.5
View on Amazon
P3 P4400 Kill A Watt Electricity Usage Monitor

P3 P4400 Kill A Watt Electricity Usage Monitor

$30.684.6
View on Amazon
Govee Dual Smart Plug 2 Pack, 15A WiFi Bluetooth Outlet, Work with Alexa and Google Assistant, 2-in-1 Compact Design Bundle with Govee Smart Plug, WiFi Plugs Work with Alexa & Google Assistant

Govee Dual Smart Plug 2 Pack, 15A WiFi Bluetooth Outlet, Work with Alexa and Google Assistant, 2-in-1 Compact Design Bundle with Govee Smart Plug, WiFi Plugs Work with Alexa & Google Assistant

$48.984.9
View on Amazon
Klein Tools MM400 Multimeter, Digital Auto Ranging, AC/DC Voltage, Current, Capacitance, Frequency, Duty-Cycle, Diode, Continuity, Temp 600V

Klein Tools MM400 Multimeter, Digital Auto Ranging, AC/DC Voltage, Current, Capacitance, Frequency, Duty-Cycle, Diode, Continuity, Temp 600V

$32.994.4
View on Amazon
HUANCHAIN 50 FT 12/3 Gauge Heavy Duty Outdoor Extension Cord Waterproof with Lighted end, Flexible Cold-Resistant 3 Prong Electric Cord Outside, 15Amp 1875W 12AWG SJTW, Yellow, ETL

HUANCHAIN 50 FT 12/3 Gauge Heavy Duty Outdoor Extension Cord Waterproof with Lighted end, Flexible Cold-Resistant 3 Prong Electric Cord Outside, 15Amp 1875W 12AWG SJTW, Yellow, ETL

$41.994.8
View on Amazon
Surge Protector Power Strip - HANYCONY 8 Outlets 4 USB (2 USB C) Charging Ports, Multi Plug Outlet Extender, 5Ft Braided Extension Cord, Flat Plug Wall Mount Desk Charging Station for Home Office ETL

Surge Protector Power Strip - HANYCONY 8 Outlets 4 USB (2 USB C) Charging Ports, Multi Plug Outlet Extender, 5Ft Braided Extension Cord, Flat Plug Wall Mount Desk Charging Station for Home Office ETL

$9.994.8
View on Amazon
Jackery Explorer 500 v2 Portable Power Station, 512Wh LiFePO4 Battery, 500W AC/1000W Peak, Solar Generator for Camping, Outdoors, and Power Outages

Jackery Explorer 500 v2 Portable Power Station, 512Wh LiFePO4 Battery, 500W AC/1000W Peak, Solar Generator for Camping, Outdoors, and Power Outages

$339.004.5
View on Amazon
P3 P4400 Kill A Watt Electricity Usage Monitor

P3 P4400 Kill A Watt Electricity Usage Monitor

$30.684.6
View on Amazon
Govee Dual Smart Plug 2 Pack, 15A WiFi Bluetooth Outlet, Work with Alexa and Google Assistant, 2-in-1 Compact Design Bundle with Govee Smart Plug, WiFi Plugs Work with Alexa & Google Assistant

Govee Dual Smart Plug 2 Pack, 15A WiFi Bluetooth Outlet, Work with Alexa and Google Assistant, 2-in-1 Compact Design Bundle with Govee Smart Plug, WiFi Plugs Work with Alexa & Google Assistant

$48.984.9
View on Amazon
Klein Tools MM400 Multimeter, Digital Auto Ranging, AC/DC Voltage, Current, Capacitance, Frequency, Duty-Cycle, Diode, Continuity, Temp 600V

Klein Tools MM400 Multimeter, Digital Auto Ranging, AC/DC Voltage, Current, Capacitance, Frequency, Duty-Cycle, Diode, Continuity, Temp 600V

$32.994.4
View on Amazon

As an Amazon Associate, we earn from qualifying purchases.

Example Calculations

1Gaming PC: CPU + GPU + RAM

Inputs

CPU12V × 10A = 120W
GPU12V × 25A = 300W
RAM (2x)3.3V × 0.5A × 2 = 3.3W
Efficiency80%
Headroom20%

Result

Recommended PSU650 W
DC Load423 W
AC Draw634 W

DC = 120+300+3.3 = 423.3W. With headroom: 423.3×1.2 = 508W. AC: 508/0.8 = 635W. Round up to 650W.

2Office PC: CPU + SSD + Fans

Inputs

CPU12V × 5A = 60W
SSD5V × 0.5A = 2.5W
Fans (3x)12V × 0.3A × 3 = 10.8W
Efficiency80%
Headroom20%

Result

Recommended PSU150 W
DC Load73 W
AC Draw110 W

DC = 60+2.5+10.8 = 73.3W. With headroom: 73.3×1.2 = 88W. AC: 88/0.8 = 110W. Round up to 150W.

Frequently Asked Questions

Q

How do I calculate power supply wattage?

Add up watts for each component: W = V × I. Then add headroom (20%) and divide by PSU efficiency (80%). Example: 300W load × 1.2 headroom / 0.8 efficiency = 450W PSU.

  • Sum component watts: Σ(V × I)
  • Add 20% headroom for spikes
  • Divide by efficiency (80-90%)
  • Round up to nearest standard PSU size
ComponentVoltageCurrentPower
CPU12V10A120W
GPU12V25A300W
RAM (2x)3.3V0.5A3.3W
5 Fans12V0.3A18W
Q

What PSU efficiency should I use?

80 PLUS rated PSUs: White = 80%, Bronze = 82-85%, Gold = 87-90%, Platinum = 92-94%, Titanium = 96%. Higher efficiency wastes less power as heat.

  • 80 PLUS White: 80% at 50% load
  • 80 PLUS Bronze: 82-85%
  • 80 PLUS Gold: 87-90%
  • 80 PLUS Platinum: 92-94%
Q

How much headroom should I add?

20% headroom is standard for steady loads. For gaming PCs with GPU power spikes, use 25-30%. For servers with UPS, 40% headroom ensures startup current handling.

  • Desktop/office: 20% headroom
  • Gaming PC: 25-30% for GPU spikes
  • Server: 30-40% for reliability
  • Overclocking: add 10% extra
Q

Can I use a PSU that is too powerful?

An oversized PSU works fine but wastes money. PSUs are most efficient at 40-60% load. A 1000W PSU at 200W load runs at lower efficiency than a 500W PSU at the same load.

  • Oversized PSU: works but less efficient at low load
  • Peak efficiency at 40-60% rated load
  • Undersized: crashes, shutdowns, damage
  • Match PSU to actual usage

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Last Updated: Jun 18, 2026

This calculator is provided for informational and educational purposes only. Results are estimates and should not be considered professional financial, medical, legal, or other advice. Always consult a qualified professional before making important decisions. UseCalcPro is not responsible for any actions taken based on calculator results.

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