Speed Analyst

Fast on paper, laggy in practice? Test for bufferbloat.

A speed test can look perfect while video calls stutter and games lag. A common cause is bufferbloat: your latency climbing sharply whenever the connection is under load. The number that matters is the delta — loaded latency minus idle latency.

How to read your result

Run the test while nothing else heavy is using your connection. An idle ping of 12 ms that jumps to 250 ms under load is a +238 ms delta — enough to ruin a video call even on a fast plan. Under +30 ms is excellent (LibreQoS grades it A) and 30–60 ms is still good (B); once you push past +60 ms it starts to bite (C or worse) and your router's queue management needs attention — see "How to fix bufferbloat" below.

The LibreQoS test grades your connection from A+ to F and shows how it would hold up for gaming, video calls and streaming while the link is busy — not just the raw speed number. It uses a globally distributed test infrastructure, so you're normally measuring your connection rather than the distance to a far-away test server.

Run the LibreQoS test ↗ or the advanced view (per-direction numbers) ↗

Waveform’s Bufferbloat Test is another good one — LibreQoS’s test was in fact inspired by it. We use LibreQoS (above), but either will show you latency under load.

Illustration · example result
IDLE 12 ms
LOADED 187 ms
Δ +175 ms — significant bufferbloat
Test on a wired computer if you can. Plug into the router with an Ethernet cable before testing. Over Wi-Fi you're partly testing your wireless, not your line — poor Wi-Fi conditions can drag the result down and make a healthy connection look bad. Wired gives the clearest picture of what the connection itself can do — though even a wired path can be throttled by the hardware in between. No Ethernet port? A USB-to-Ethernet adapter works. Can only test over Wi-Fi? Treat a poor result as "could be Wi-Fi or the line," then use the Wi-Fi guide to check.

How to fix bufferbloat

The fix is to move the bottleneck off your ISP's buffer (which you can't control) and onto your own router (which you can) — by shaping your traffic to just under your real line speed, so a smart queue can keep latency low under load.

Enable Smart Queue / SQM

If your router has a Smart Queue, SQM, Adaptive QoS or Bufferbloat setting, turn it on and enter your speeds — set them to about 90% of what you actually measured, not your plan's headline figure. If it offers an algorithm choice, CAKE is generally the preferred choice on home connections, with fq_codel a close second. ("SQM" / "Smart Queue" is the feature; CAKE and fq_codel are the queue algorithms it runs.)

Why 90%? It makes your router the bottleneck instead of your ISP's equipment. Once your router is the slowest point in the path, its smart queue decides which packets wait — instead of leaving that decision to a large unmanaged queue upstream.

A caveat on hardware: a smart queue runs in the router's CPU, inspecting and shaping every packet in software rather than offloading to hardware — so it's processor-intensive. A Raspberry Pi-class device or a mid-range router shapes a 100 Mbps line easily, but a low-end consumer router can run out of CPU on a 250 Mbps or gigabit plan — it won't crash, it simply can't shape that fast, so throughput bottlenecks below your line rate and latency can creep back up. If turning SQM on caps your speed, the router's CPU is the limit: lower the shaped rate, or move to hardware with more headroom.

No SQM option? Just rate-limit

Even a plain bandwidth limit helps, because it's the same mechanism. Cap your router's rate to about 90% of measured. Upload usually matters most — on asymmetric plans, where upload is much slower than download, the uplink buffer fills first — so if you can only limit one direction, limit upload. If your router offers none of this, first make sure it's running the latest manufacturer firmware — vendors sometimes add a Smart Queue or QoS option in a later release (and it's worth doing for security regardless). Still nothing? The simplest fix is a router that does SQM out of the box — many mid-range and "gaming" routers, and a lot of mesh systems, now include it. (Flashing open firmware like OpenWrt on a supported model also unlocks it, but that's an advanced project with a genuine risk of rendering the router unusable (“bricking”) if something goes wrong, so it's only worth it if you're comfortable with that.) Re-run the test after each change — you want loaded latency to stay close to idle.

Wire the things that can't tolerate lag

For devices where real-time response matters most — gaming consoles and PCs, work-from-home machines on video calls, VoIP handsets, streaming boxes — a wired Ethernet connection is the biggest single reliability win. It avoids Wi-Fi's airtime contention and jitter entirely, giving lower and steadier latency. Leave Wi-Fi for the phones, tablets and roaming devices that genuinely need to be wireless.