CPU or GPU bottleneck: which one is limiting your games?

How a frame gets made

For every frame, the processor works out what happens — game logic, physics, what to draw — and hands the drawing to the graphics card. The two work at the same time on different frames, so the slower of the two sets the frame rate. When the graphics card is the slower one, it is busy almost all the time. When the processor is, the graphics card finishes early and waits for its next piece of work.

Signs the graphics card is the limit

• Graphics card usage sits at 95–100% while you play.
• Lowering the resolution or the graphics settings raises the frame rate a lot.

This is normal, and in most games it is what you want: the most expensive part in the machine is the one doing the work. It only matters when the frame rate is lower than you would like.

Signs the processor is the limit

• Graphics card usage stays well below 90% while the frame rate is under your target, and nothing is capping it.
• Lowering the resolution barely changes the frame rate.
• One or two processor threads are close to 100%, even though total CPU usage looks low.

Total CPU usage is the number that misleads people most. Many games do much of their work on one main thread, and one thread running flat out on a 16-thread processor adds only about 6% to the total. To see the threads, open Task Manager, choose Performance → CPU, right-click the graph and choose Change graph to → Logical processors.

The resolution test

The quickest check needs no tools. Note the frame rate in one place in the game, then lower the resolution (or the game’s render scale) and look again, changing nothing else. If the frame rate rises a lot, the graphics card was the limit. If it hardly moves, the processor was — or something is capping it.

Rule out a cap first

If the frame rate sits on a round number — 60, 144, 165 — something is probably capping it: V-Sync, a frame limiter in the game or the graphics driver, or the monitor’s refresh rate. A cap is not a bottleneck, and a monitor left at 60 Hz is one of the most common reasons a fast PC looks slow.

Settings that imitate a hardware limit

Before blaming either part, rule out the causes that cost nothing to fix. Each one makes the hardware look slower than it is:

• Memory running below its rated speed, or in single channel — which makes the processor look slow, especially in the slowest frames.
• A power plan that limits the processor, turbo boost switched off, or a laptop running on battery.
• Overheating, which makes the processor or the graphics card slow itself down.
• A monitor plugged into the motherboard instead of the graphics card, so the game runs on the processor’s own graphics.
• A graphics card running on fewer PCIe lanes than it should, for example because it is in the wrong slot.
• Background applications holding processor time or graphics memory.
• Hardware-accelerated GPU scheduling switched off. On recent NVIDIA cards, DLSS Frame Generation needs it.

Measure it properly

The resolution test tells you which part is the limit on average. Frame-by-frame measurement tells you how often. Intel’s free PresentMon records, for every frame, how long the processor and the graphics card each spent on it. When the graphics card was busy for nearly the whole frame, it set the pace; when the processor was, it did. Counted over a few minutes of play, that becomes a share: the graphics card set the pace for 85% of frames, say, and the processor for the rest.

That is what Bottleneck’s game measurement does, using PresentMon. With Bottleneck open, start the game and press Ctrl+Shift+F11 to begin, play for a few minutes, then press it again to finish — tones confirm each step, so you never leave the game. It reads the event tracing Windows already keeps; nothing is injected into the game. Which part held the game back, and the average frame rate, are free. Pro adds the slowest-frame figures, stutter, the full breakdown and before-and-after comparisons.

What about bottleneck calculators?

Websites that take a processor and a graphics card and return a bottleneck percentage are estimating from the part names. They cannot see your memory settings, power plan, temperatures, monitor or the game you play — which is where most real problems are. Treat them as a rough guide at most.

Before you buy anything

Fix the free things first; they often move more than an upgrade would. If the processor is still the limit in the games you actually play, a faster processor is the upgrade that helps — and in processor-limited games, large-cache chips such as AMD’s X3D models are especially effective. If the graphics card is the limit and the frame rate is below what you want, a faster card is.

Bottleneck holds back upgrade advice while a free fix is worth more, and when it does suggest a part, it says what the change would buy you.