How to plan your first PC build: budget split, compatibility checks and common mistakes

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Building your own PC is easier than it looks: the parts only fit one way, and the hard part is not the screwdriver work but the planning. Get the parts list right and the build itself is an afternoon. This guide deliberately avoids naming current models or prices, which change every few months, and focuses on how to decide.

Start with what you will use it for

Write down the two or three things you will actually do with the PC, and at what resolution or scale. The answer decides where the money goes.

Gaming: the graphics card (GPU) matters most. As a rough rule, many builders put the largest single share of the budget, often around a third or more, into the GPU.
Video editing, 3D rendering, programming with big builds: more CPU cores and more RAM pay off, and the GPU matters for some editing and rendering software.
Office, browsing, study: a modest CPU with integrated graphics, a fast SSD and enough RAM is plenty. Spending more will not make it feel faster.
Streaming while gaming: a balance of a strong GPU and a capable CPU.

Check which monitor you will use. A high-refresh-rate screen at a high resolution needs far more GPU power than a standard one.

Balancing CPU and GPU

A mismatched pair wastes money. A top-end graphics card held back by an entry-level processor, or the other way round, means you pay for performance you never see. Look at benchmarks for the specific games or software you use, at your resolution. At higher resolutions the GPU does more of the work; at lower resolutions with very high frame rates, the CPU matters more.

Choosing the power supply (PSU)

The PSU is the part beginners skimp on most often, and a poor one can take other parts with it when it fails.

Add up the power draw of your CPU and GPU (the manufacturers list it), add a margin for the rest of the system, and choose a PSU with comfortable headroom above that. Many builders aim for the PSU's typical load to sit well below its maximum.
GPU makers publish a recommended PSU wattage for each card. Use it as a minimum.
Buy from a reputable brand with a good warranty, and look for an efficiency rating. Check reviews of the specific model, not just the brand.
Make sure it has the power connectors your graphics card needs.

Compatibility checks before you buy

CPU socket and motherboard: the processor must match the motherboard's socket and chipset. Check the motherboard's CPU support list, and whether an older board needs a BIOS update for a newer chip.
RAM type: motherboards support one generation of memory (for example DDR4 or DDR5), not both. Check the board's supported speeds, and buy RAM in a matched kit.
Form factor: the motherboard size (ATX, Micro-ATX, Mini-ITX) must fit the case.
GPU length and thickness: check the case's maximum graphics card length and how many slots the card occupies.
CPU cooler height: tall air coolers may not fit narrow cases. If you choose a liquid cooler, check the case has room for the radiator.
Storage: count M.2 slots for NVMe SSDs, and check whether using one disables any SATA ports.
PSU size: small cases may need a smaller power supply format.

Online parts-list builders flag many of these clashes automatically, but read the manuals and spec sheets for the ones that matter.

Where first-time builders go wrong

Plugging the monitor into the motherboard instead of the graphics card, and wondering why games run badly.
Forgetting to enable the memory's rated speed profile in the BIOS, so RAM runs slower than it should.
Installing RAM in the wrong slots. The manual shows which two to use for a pair.
Forgetting the motherboard standoffs, or leaving the plastic film on the cooler.
Not plugging in the CPU power cable at the top of the board.
Buying too few case fans, or pointing them all the same way.
Overspending on the motherboard and underspending on the GPU or PSU.
Building on carpet. Work on a hard table and touch something metal to discharge static first.

Before the first power-on

Do a test with only the essentials connected if you can. If it does not start, recheck the power cables, reseat the RAM and look at the motherboard's diagnostic lights. Most first-boot problems are a loose cable. Post your planned parts list or ask about your use case in the comments, and others can sanity-check it.