How Pulse measures your speed

Version 6 methodology. Written by Dr Alex J Martin-Smith (LinkedIn), BroadbandSwitch.uk. Last reviewed 15 October 2026.

The test, start to finish

1. Connect. The page asks the test edge for its own view of your connection: your public IP address, the network it belongs to, an approximate city and which Cloudflare location you reached. Nothing is stored by UKSpeedTest.
2. Ping. After one warm-up request, Pulse sends a series of tiny requests (9 in Quick, 15 in Standard, 25 in Thorough) and times each round trip. Where the browser allows it, the time is taken from the Resource Timing API, from the moment the request leaves to the moment the first byte of the reply arrives, and the edge's own processing time (reported in its Server-Timing header) is subtracted. Ping is the median; jitter is the average gap between consecutive samples.
3. Download. Several streams (4 in Quick, 5 in Standard, 6 in Thorough) each fetch 25 MB from the edge over and over until time is up. Every 250 ms Pulse counts the bytes that arrived across all streams and converts them to megabits per second. If the line is running above 300 Mbps after two seconds, extra streams are added, up to eight, so gigabit lines are not under-read.
4. Upload. Three to five streams post 8 MB blocks of data to the edge until time is up. The browser reports bytes as it sends them, which is why the first second of upload can look a little high; the ramp-up rule below takes care of that.
5. Loaded pings. In Standard and Thorough modes the same tiny ping requests keep going every 400 ms while the download and upload run. The rise in ping while the line is busy is what the busy-line grade measures.

How the headline numbers are worked out

Download and upload

The first quarter of each transfer is treated as ramp-up and ignored: connections open, TCP windows grow and browsers buffer. From the rest, Pulse takes a trimmed mean: the 250 ms samples are sorted, the lowest 10% and highest 10% are dropped, and the remainder averaged. This sits between a plain average (which a stall drags down) and a peak (which flatters a line). The fastest moment and the 10th to 90th percentile range are shown under "All the numbers".

Ping and jitter

Ping is the median of the idle samples. Jitter is the mean absolute difference between consecutive samples. The best single sample is also shown, as is the round trip the edge itself observed at the TCP layer where it reports one.

Busy-line grade

Pulse compares the median ping while the line was loaded (the higher of the download and upload phases) with the idle median. The rise is graded on Pulse's own bands: A under 30 ms, B under 60 ms, C under 120 ms, D under 250 ms, F 250 ms or more. The problem it detects is usually called bufferbloat. A line with a D or F will feel fine for one person streaming and terrible the moment someone else starts a download.

Speed bands

Download results are labelled using Ofcom's public definitions where they exist: under 10 Mbps is below the universal service obligation (USO) minimum, 30 Mbps and above is superfast, 300 Mbps and above is ultrafast, and 900 Mbps and above is labelled gigabit. The bands in between (Standard 10 to 30, Superfast 30 to 100, Fast 100 to 300) are Pulse's own, chosen to match how UK packages are sold.

What is and is not measured

Why your result can differ from other tests

• Server distance. Pulse uses the nearest Cloudflare edge. A test that picks a server inside your own provider's network can show a lower ping and a slightly higher speed.
• Number of streams. Single-stream tests under-read fast lines; Pulse uses several streams and adds more when the line is quick.
• How the number is averaged. Some tests report a peak, some a plain average. Pulse reports a trimmed mean of the steady part, which is deliberately conservative.
• Browser and device. Older phones and laptops can struggle to process a gigabit stream. If a wired PC shows far more than a phone, the phone is the limit, not the line.
• Time of day. UK lines are busiest between 8pm and 10pm. Advertised speeds are measured in that window, so it is the fairest time to compare.

Data use and fairness to your connection

Time-based tests use more data on faster lines. As a guide, Standard mode uses roughly 60 MB on a 50 Mbps line, about 350 MB on a 300 Mbps line and between 1 and 2 GB on a gigabit line, download and upload combined. The exact figure for each test is shown under "All the numbers". On mobile data, or when the browser's data saver is on, Pulse defaults to Quick mode and will not start on its own.

Privacy

Everything is calculated in your browser. UKSpeedTest has no server component in the test and receives no results. The test edge sees your IP address in the ordinary way any website does; Cloudflare's handling of it is covered by Cloudflare's privacy policy. If you allow optional storage in the cookie settings, your last 20 results are kept in your own browser only, and you can clear them from the results panel. Full details are in our privacy policy.

Limits worth knowing

• One run is a snapshot. Two or three runs at different times tell you far more than one.
• Wi-Fi tests measure your Wi-Fi as much as your broadband. A cable to the router isolates the line.
• A VPN, a corporate proxy or a browser extension that blocks requests to speed.cloudflare.com will give low or empty results.
• Pulse reports decimal megabits per second (1 Mbps = 1,000,000 bits per second), the unit UK providers advertise in. File sizes on your computer are in bytes; divide Mbps by 8 for MB per second.

Changes in version 6 (October 2026)

• Upload speed added.
• Ping under load and the busy-line grade added for Standard and Thorough modes.
• Download changed from nine fixed 20 MB passes to several parallel streams for a fixed time, with the trimmed-mean headline described above. This is faster, uses less data on slower lines and reads fast lines more accurately.
• Quick, Standard and Thorough test lengths added.
• Connection details now come from the test edge rather than a separate IP lookup service, removing one third party from the page.

Related

• Run the Pulse speed test
• How to run an accurate broadband speed test
• Latency test: ping, jitter and bufferbloat
• Upload speed test: what a good upload looks like
• How Pulse compares with other UK speed tests
• Live broadband quality monitor on BroadbandSwitch.uk

References

1. Ofcom. (n.d.). Broadband speeds: codes of practice. ofcom.org.uk
2. Ofcom. (2023, August 8; updated 2026). Your right to request a decent broadband service. ofcom.org.uk
3. W3C. (2024). Resource Timing. w3.org
4. Cloudflare. (n.d.). Cloudflare speed test. speed.cloudflare.com