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Yes, k6 can run in an environment capped at 512 MB, but that number alone cannot tell you how many virtual users (VUs) your test can support. Memory use depends on the script, its dependencies, VU count, and the generator environment. Treat 512 MB as a limit on your specific container, VM, or host—not as a universal k6 limit—and measure a representative test before relying on a VU estimate.
What 512 MB means for a k6 test
A 512 MB ceiling describes the resources available to a particular load generator; Grafana’s k6 documentation does not establish it as a product-wide memory limit. First identify what the cap actually covers: a container limit, VM allocation, host budget, or another constraint. Confirm whether it is decimal MB or binary MiB and whether the limit applies to k6 alone or the entire environment. The deployment configuration, not the k6 documentation, determines those details.
This distinction matters because a load generator is part of the test. If its memory, CPU, or network becomes saturated, it may fail to produce the requested load or may affect response-time results. A result is useful only if the generator can sustain the intended work. Grafana’s guidance on running large tests recommends monitoring generator resources and keeping memory use below 90% of available physical RAM. For a 512 MB budget, 90% is 460.8 MB (512 × 0.9); that is a calculation from the recommendation, not a separate published k6 statistic.
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How much RAM does k6 need per VU?
Grafana’s current k6 documentation gives a planning baseline of about 1–5 MB of RAM per VU for simple tests, with the amount depending on script complexity and dependencies. It gives the corresponding rough illustration that 1,000 VUs may require 1–5 GB for a simple test. These are planning estimates, not guarantees for every workload. The live documentation was accessed on October 7, 2026, and does not state a publication date.
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VUs do not have a fixed memory cost. JavaScript dependencies and script complexity affect RAM use, while file uploads and large JavaScript modules can use substantially more memory per VU than a simple script. Fixed process overhead also means that multiplying the per-VU range by your target count is only an approximation. See Grafana’s k6 guidance on OS fine-tuning and memory and its large-test planning guidance.
Estimate capacity with a representative run
Use the actual test script and generator environment to establish a starting point. A modest run—for example, one at 100 VUs—can show how memory behaves for your workload, but it does not prove that a much larger run will scale linearly. Keep the same modules, data handling, request pattern, and checks you intend to use in the target test.
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- Define the budget. Record the configured limit, its units, and whether it covers the k6 process or the whole environment.
- Run representative work at modest load. Use the real script, dependencies, data, requests, and checks rather than a simplified stand-in.
- Measure the generator. Record memory, CPU, and network utilization alongside k6 output. Treat the observed memory as a starting point, not a guaranteed per-VU rate.
- Estimate cautiously. Use the run to inform a target-load estimate, allowing for fixed overhead and workload differences. Increase load in stages and watch for resource pressure.
Reduce avoidable memory use
Discard response bodies you do not use
If the script neither reads nor asserts against response bodies, set discardResponseBodies: true in the k6 options. This can reduce memory use. Do not discard bodies that later script steps or checks need. Grafana documents this setting and other optimization guidance in its large-test guide.
Review script and data costs
Look for large JavaScript dependencies, file uploads, per-VU data copies, and custom metrics that may be material to the test’s memory footprint. These are not automatically problems to remove: retain what represents the real workload, but avoid loading or copying data that the script does not need.
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Check that the generator delivered the intended load
Monitor the generator throughout the run, not just before it starts or after it finishes. Compare observed memory with the environment’s cap and the below-90% physical-memory guidance, and track CPU and network utilization as well. If the generator approaches its limit, note that when interpreting the result.
Use k6 metrics such as http_reqs for request count, http_req_failed for failed requests, and http_req_duration for request duration. These describe test output; by themselves, they do not prove the generator was unconstrained. Report both the intended load and whether the generator maintained it, along with any dropped or incomplete work. The metric definitions are in k6’s metrics documentation.
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When to use more than one generator or cloud execution
If a constrained local generator cannot sustain the load you need, scaling execution elsewhere is an option—not a guarantee that a particular service or configuration is available to you. Grafana documents running locally while streaming a test to k6 Cloud, including options to avoid duplicate local threshold and terminal-summary processing. Consult the documented local and cloud execution guidance and verify the execution mode, account access, and current product behavior before choosing it.
Whether you stay local or scale out, assess whether the setup can reach the desired load, has enough memory, CPU, and network headroom, and represents the geography and network path of the workload. Also consider where results and thresholds are processed and the operational complexity of the setup. A larger distributed test can answer a different question if its network path does not represent the users or systems you intend to model.
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