PSU Calculator

About PSU Calculator

How the Wattage Estimate Works

Each component adds its TDP (thermal design power) or typical power consumption to a running total. A 50W baseline covers motherboard, chipset, and VRM overhead. The calculator then multiplies by 1.2 for headroom and rounds up to the nearest standard PSU size.

Component	Typical Power Range	What Affects It
CPU	65-253W	Core count, clock speed, architecture. Intel 14th Gen K-series up to 253W, AMD Ryzen 9000 series 65-170W
GPU	75-600W	GPU tier and generation. RTX 4060 at 115W, RTX 4090 at 450W, RTX 5090 at 575W
RAM	3-10W per stick	DDR4 about 3-5W per DIMM, DDR5 about 4-8W per DIMM
SATA SSD	2-5W	Read/write activity level
NVMe SSD	5-12W	PCIe Gen 4/5, active read/write can spike higher
HDD	6-12W	Spin speed (5400 vs 7200 RPM), 3.5" vs 2.5"
Case fans	1-5W each	Size, RGB lighting, speed
AIO pump	5-15W	Pump speed and model
Motherboard + chipset	30-80W	Higher for enthusiast boards with many features

Why 20% Headroom Matters

Modern GPUs draw power in sharp transient spikes that can exceed the rated TDP by 50% or more for fractions of a second. NVIDIA calls these "transient power excursions." If the PSU cannot handle these spikes, the system triggers an overcurrent protection shutdown - the PC simply turns off during a game or benchmark. The 20% recommendation accounts for these spikes and gives room for future upgrades.

GPU	Rated TDP	Measured Transient Spikes	Recommended Minimum PSU (with CPU)
RTX 4060	115W	Up to 170W	550W
RTX 4070 Ti	285W	Up to 350W	700W
RTX 4080	320W	Up to 420W	750W
RTX 4090	450W	Up to 600W	850-1000W
RX 7800 XT	263W	Up to 310W	650W
RX 7900 XTX	355W	Up to 430W	800W

Standard PSU Sizes

Power supplies come in standard wattage steps. The calculator rounds up to the nearest one:

Wattage	Typical Build	Price Range (80+ Gold)
450W	Office PC, HTPC, no dedicated GPU	$40-60
550W	Budget gaming (RTX 4060, RX 7600)	$50-80
650W	Mid-range gaming (RTX 4070, RX 7800 XT)	$60-100
750W	High-performance gaming (RTX 4070 Ti, RX 7900 XT)	$80-120
850W	High-end gaming (RTX 4080, overclocked builds)	$100-150
1000W	Enthusiast (RTX 4090, dual GPU workstations)	$130-200
1200W	Extreme builds, heavy overclocking	$180-280
1600W	Multi-GPU, server-class workloads	$300-500

80 Plus Efficiency Ratings

The 80 Plus certification tells you how efficiently the PSU converts AC wall power to DC power for your components. Higher efficiency means less wasted electricity and less heat.

Rating	Efficiency at 20% Load	Efficiency at 50% Load	Efficiency at 100% Load	Best For
80 Plus (White)	80%	80%	80%	Budget builds where cost is the priority
80 Plus Bronze	82%	85%	82%	Budget to mid-range gaming PCs
80 Plus Gold	87%	90%	87%	Most gaming and workstation builds (best value)
80 Plus Platinum	90%	92%	89%	Enthusiast builds, systems running 24/7
80 Plus Titanium	92%	94%	90%	Servers, workstations with high electricity costs

Gold is the sweet spot for most builders. The jump from Bronze to Gold saves meaningful energy over a year. The jump from Gold to Platinum saves less while costing significantly more. For a look at electricity costs over time, check the electricity cost calculator.

Modular vs Non-Modular

Type	How It Works	Pros	Cons
Non-modular	All cables permanently attached	Cheapest option	Unused cables clutter the case, harder to manage airflow
Semi-modular	Main cables (24-pin, CPU) attached; others detachable	Good balance of price and tidiness	Still has some fixed cables you might not use
Fully modular	All cables detachable	Cleanest builds, only use what you need, easier to upgrade cables	Costs more, cables are not interchangeable between brands

Important: never mix modular cables between different PSU brands or even different models from the same brand. The pin layouts can differ, and using the wrong cable can destroy components.

ATX 3.0, ATX 3.1, and the 12VHPWR Connector

ATX 3.0 (released by Intel in February 2022) and the revised ATX 3.1 spec (May 2024) introduced the 12VHPWR and 12V-2x6 connectors, which deliver up to 600W of GPU power through a single cable. NVIDIA RTX 4000 and 5000 series GPUs use these connectors. ATX 3.0 and 3.1 PSUs are also rated to handle transient power spikes of up to 200% of their rated wattage for short durations, which is the main reason they are recommended for modern high-end GPUs. Older ATX 2.x PSUs require a bundled adapter from three or four 8-pin PCIe connectors. The adapters work, but the 12V-2x6 revision in ATX 3.1 slightly shortens the sense pins so that partially-seated cables no longer attempt to draw full power - a change introduced after several high-profile melted-connector incidents on the RTX 4090 in late 2022 and early 2023. If you are building new with a 4070 Ti or higher, prefer an ATX 3.1 unit.

Worked Example: Mid-Range Gaming Build

Take a build with a Ryzen 7 7700X (105W), an RTX 4070 Super (220W), 2x 16GB DDR5 (10W), a 1TB NVMe SSD (7W), no HDD, 4 case fans (12W), and an AIO pump (10W). Adding a 50W motherboard baseline gives a raw draw of 414W. Multiplying by 1.2 for headroom yields 497W. The calculator rounds up to the nearest standard size, which is 550W. If you plan to upgrade to an RTX 5080-class card later, bumping to 750W avoids having to replace the PSU during the next upgrade cycle. For energy costs across a year of use, plug the wall draw into the electricity cost calculator.

What Is a Single-Rail vs Multi-Rail PSU?

A single-rail PSU routes all +12V power through one electrical rail with a combined amperage limit (e.g. 62A = 744W). A multi-rail PSU splits the +12V output into two or more independent rails with per-rail current limits (typically 20-40A each, or 240-480W per rail). Single-rail is more common in modern consumer PSUs because GPU manufacturers prefer a single high-capacity rail to handle transient spikes without tripping overcurrent protection. Multi-rail offers an extra safety margin in the event of a short circuit - the affected rail trips first instead of dumping the full PSU output into the fault. Both are safe when built to specification; the choice rarely matters for typical home builds.

How Much Does PSU Efficiency Save Per Year?

The difference between 80 Plus Bronze and 80 Plus Gold is about 5 percentage points of efficiency at typical loads. For a gaming PC drawing 400W under load and running 4 hours per day year-round, Bronze (85% eff.) pulls 470W from the wall while Gold (90% eff.) pulls 444W - a saving of 26W for 1,460 hours, or about 38 kWh per year. At the April 2026 UK domestic price cap of 27.03p per kWh (Ofgem, April-June 2026), that is around GBP 10 per year. In the US at an average residential rate of about 16.5c per kWh (EIA, January 2026), it is roughly USD 6.30. Gold typically costs USD 20-30 more than Bronze, so the payback is 2-4 years. Platinum and Titanium rarely pay back on consumer loads; they make more sense for 24/7 servers and high-electricity-price regions.

Common PSU Mistakes

Mistake	Why It Happens	What to Do Instead
Buying the cheapest no-name PSU	Looks like a good deal	Stick to reputable brands with proper certification and protections
Sizing for exactly the calculated wattage	Trying to save money	Always add 20%+ headroom for spikes and upgrades
Reusing old PSU cables with a new PSU	Cables look identical	Always use the cables that came with your specific PSU model
Ignoring the 12V rail amperage	Only looking at total wattage	Check the 12V rail capacity - it powers the CPU and GPU
Daisy-chaining PCIe power cables	Using one cable for two GPU connectors	Use separate cables for each GPU power connector when possible

To check whether your CPU and GPU are a balanced pairing, the bottleneck calculator compares tiers at different resolutions. For overclocking power estimates, the overclocking calculator shows how voltage and frequency affect power draw. All calculations run in your browser with no data sent anywhere.

Sources

• Intel - ATX 3.0 Multi-Rail Desktop Power Supply Design Guide
• Clearesult - 80 PLUS Certification Program Details and Efficiency Levels
• NVIDIA - GeForce RTX 40 Series TDP and Power Requirements
• AMD - Ryzen Desktop Processor TDP Specifications
• Ofgem - UK Domestic Energy Price Cap (April-June 2026)
• US Energy Information Administration - Average Residential Electricity Price
• PCI-SIG - PCIe CEM and 12V-2x6 Connector Specification