When building a custom gaming PC, it’s important to choose components that work well together to avoid performance bottlenecks. A bottleneck occurs when one component, like the CPU or GPU, limits the performance potential of the other components.Online bottleneck calculators aim to help identify potential bottlenecks, but they have significant limitations. Here’s what you need to know about using bottleneck calculators for your custom PC build.

How Bottleneck Calculators Work

Bottleneck calculators, like those from PC BuildsΒ and CPU Agent, allow you to input a CPU and GPU combination. They then estimate the relative performance of the CPU vs GPU to predict if either component will significantly bottleneck the other.Most calculators let you specify the target resolution (e.g. 1080p vs 4K) and workload type (e.g. gaming vs productivity) to refine the bottleneck prediction. The calculators use benchmark data to generate a bottleneck percentage for the given hardware combination and workload.

Limitations of Bottleneck Calculators

While bottleneck calculators can provide a rough starting point, they have major limitations:

  • Inaccurate predictions: The bottleneck percentages are synthetic estimates that often don’t match real-world performance. Actual bottlenecks vary significantly based on the specific game/application, graphics settings used, and the benchmark scene.
  • Incomplete system info: Calculators only look at CPU and GPU, ignoring other impactful components like RAM speed/capacity, storage, and cooling that affect bottlenecks.
  • Questionable data sources: Many calculators allow users to submit their own benchmark results, making the underlying data set unreliable.
  • Misleading upgrade recommendations: Calculators may suggest expensive and unnecessary upgrades, like recommending a 12-core CPU over a 6-core for gaming when extra cores provide no benefit.

As one Reddit user put it, “bottleneck calculators are trash” and “only exist to scare you into buying from affiliate links”.Β While that may be an exaggeration, it’s clear bottleneck calculators are far from definitive.

Making Informed Decisions for Your Custom PC

Instead of relying on bottleneck calculators, it’s best to research benchmark results from reputable sources for the types of games and applications you plan to run. Look for CPU and GPU benchmarks at your target resolution and settings.Ideally, pair your CPU and GPU so that both are utilized over 90% in demanding scenarios. Some bottlenecking is expected and normal. The key is avoiding extreme bottlenecks, like pairing a high-end GPU with an entry-level CPU.Be sure to choose a balanced overall system with sufficient RAM capacity and speed, an SSD, and quality cooling. Don’t forget a variable refresh rate monitor to reduce stuttering from minor CPU bottlenecks.


While bottleneck calculators promise a simple answer, the reality of PC building is more nuanced. Component interactions are complex and vary based on workload. Use bottleneck calculators as a starting point if you must, but put more weight on real-world benchmarks and system balance. With proper research, you can build a custom PC that performs to your expectations without wasting money on unnecessary components.

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