Free tools
Free load testing calculators
Free, browser-based calculators for planning load tests: convert traffic into concurrent users and requests per second, size virtual users and pacing, compute p95/p99 from raw latencies, and turn an SLO into an error budget. Nothing to install and no sign-up; everything runs locally in your browser.
Calculators
Concurrent Users CalculatorTurn monthly or daily sessions, session length and peak-hour share into average and peak concurrent users, then into RPS, using Little's Law (L = λ·W).Free toolRequests per Second (RPS) CalculatorCalculate average, peak and target requests per second from daily requests or users, a peak factor and headroom. Reverse mode turns VUs into RPS.Free toolLatency Percentile Calculator (p50, p95, p99)Paste response times in ms and get p50, p90, p95, p99, p99.9, mean and a histogram. Shows nearest-rank and interpolated percentiles side by side.Free toolThink Time and Pacing CalculatorCalculate how many virtual users you need, the pacing interval per iteration and the max throughput from target RPS, response time and think time.Free toolError Budget and SLO CalculatorEnter an SLO such as 99.9% and a window to get allowed downtime, allowed failed requests and burn-rate times, then set load test error thresholds from it.Free toolApdex CalculatorCalculate Apdex from satisfied, tolerating and frustrated counts or raw latencies with threshold T. See the rating band and use it as a load test threshold.Free toolBandwidth Calculator for Load Tests and APIsConvert requests per second and response size into Mbps or Gbps, GB per load test, hour and month, and egress cost at your own $/GB, with CDN offload.Free toolDatabase Connection Pool Size CalculatorSize a database connection pool per instance from RPS, queries per request and query time, check the total against max_connections, and compare with HikariCP.Free toolServer Capacity CalculatorWork out how many servers or pods you need from peak RPS, per-instance RPS measured in a load test and target utilization, with N+1 or zone redundancy.Free toolRetry Amplification CalculatorCalculate how retries at each layer multiply load on a failing dependency: worst case, expected load at a given failure rate, and the cap from a retry budget.Free tool
How to use them together
- Size the traffic. Start with the concurrent users calculator or the RPS calculator to turn analytics numbers into a peak request rate.
- Size the test. Use the think time & pacing calculator to find how many virtual users that rate needs, or switch to an arrival-rate (RPS) test.
- Set pass/fail thresholds. Derive an allowed error rate from the error budget calculator and a latency target from your SLO.
- Read the results. Paste raw timings into the percentile calculator and follow how to read load test results.
The concepts behind the math are explained in Little's Law for load testing, virtual users vs RPS and the load testing glossary.
Run this as a real load testFree plan: 10 VUs, 50 RPS, live p95/p99 and error charts, no credit card. Starter $19/mo (250 VUs) or Pro $49/mo (2,000 VUs) with a 7-day free trial when you need more.