How is reaction time measured?

A trial starts when the ready callback records its timestamp and ends when the page's event handler records your click or key response. The randomized wait is scheduling time and is not included in a completed trial, and early responses are discarded.

What statistics are reported?

Valid trials report best, arithmetic mean, median, and spread across all accepted trials. The retained set is limited to 100 completed trials, and the five-row Recent Results section is only a view of the newest five.

Is this a measure of neurological reaction time?

No. It measures browser-observed latency from the callback that starts the prompt until your event reaches the page. Display rendering, the event loop, the operating system, and the input device can add delay, and the browser can coarsen timer resolution.

Reaction Time Calculator — Free Sports & Performance Calculator

Compare Reaction Time Calculator with related tools

All comparisons →

Reaction Time vs Half Marathon Pace CalculatorCompare browser-observed response latency across repeated visual trials against half marathon pace and even splits from a target finish time.Reaction Time vs Running PaceCompare two measured-performance tools on the sprint-performance theme: browser-observed reaction latency across repeated trials versus running pace computed from time and distance, both narrow measurements with no performance verdict.Reaction Time vs Shot Put DistanceCompare two narrow sports-analysis tools: browser-observed response latency across repeated trials versus an ideal no-air-resistance projectile scenario from entered release speed, angle, and height.Reaction Time vs Stride LengthCompare two measured-performance tools: browser-observed reaction latency across repeated trials versus step length estimated from a measured distance and counted-step trials.Reaction Time vs Swimming SpeedCompare two speed-related sports measurements: browser-observed reaction latency from repeated trials versus average swimming speed, pace per 100 meters, and projected times from distance and elapsed time.Reaction Time vs Vertical JumpCompare two measured-performance field tests: browser-observed latency across repeated reaction trials versus jump height from standing reach and three jump-reach trials.

Frequently asked questions

How is reaction time measured?: A trial starts when the ready callback records its timestamp and ends when the page's event handler records your click or key response. The randomized wait is scheduling time and is not included in a completed trial, and early responses are discarded.
What statistics are reported?: Valid trials report best, arithmetic mean, median, and spread across all accepted trials. The retained set is limited to 100 completed trials, and the five-row Recent Results section is only a view of the newest five.
Is this a measure of neurological reaction time?: No. It measures browser-observed latency from the callback that starts the prompt until your event reaches the page. Display rendering, the event loop, the operating system, and the input device can add delay, and the browser can coarsen timer resolution.

Sources

High Resolution Time Level 3
primary · Aug 10, 2026
Supports: performance.now() provides a monotonic browser clock for elapsed-time measurement; exposed resolution can be coarsened and sub-millisecond resolution is not guaranteed
— W3C High Resolution Time Level 3, vW3C Working Draft, retrieved 2026-07-10
HTML Living Standard
primary · Aug 10, 2026
Supports: clearTimeout cancels an identified pending timer; timeout callbacks are not guaranteed to run exactly on schedule and can include implementation-defined delay
— WHATWG HTML Living Standard, vLiving Standard, retrieved 2026-07-10

Related calculators

ms to Seconds ConverterConvert milliseconds to seconds or seconds to milliseconds for programming, latency, audio, sports timing, and measurement logs.6 Minute Walk Test CalculatorCompare six-minute walk distance with sex-specific predicted values, lower limits, and percentage expected using the standard 6-minute walk distance equation.Absence Percentage CalculatorCalculate employee absence percentage from scheduled employee-days and lost days, with attendance share, examples, and HR interpretation tips.Albumin Globulin Ratio CalculatorCalculate the albumin globulin ratio (A/G ratio calculation) from albumin and total protein, with the exact globulin formula, reference ranges, interpretation cautions, and sources.Annuity CalculatorModel an annuity as a stream of equal deposits or withdrawals with an opening balance, payment frequency, annual return, and ordinary or annuity-due timing.Army Body Fat CalculatorEstimate the army body fat percentage with the AR 600-9 circumference method from height, neck, waist, and (for women) hip measurements, with the age-band screening-table maxima shown for reference only.

Reaction Time Calculator