Ping, jitter & bufferbloat.
Speed isn’t why calls stutter and games lag — latency is. This checks your ping, how steady it is, and whether it spikes when the line gets busy (bufferbloat).
Downloads ~tens of MB to load the line for a few seconds. For the truest reading, test on a device wired to the router and close other downloads.
Why latency beats speed for gaming & calls
Ping is the delay before data moves — low is what makes games responsive and calls natural. Jitter is how much that delay wobbles; high jitter causes stuttery calls even on a fast line. Bufferbloat is the sneaky one: when a download saturates your line, ping can balloon from 20 ms to hundreds — so a game lags the moment someone else starts a download. A good line keeps ping steady under load; that’s what the grade measures.
Bad bufferbloat is often the router, not the ISP — a router with Smart Queue Management (SQM/QoS) usually fixes it. But a consistently high idle ping can point at the connection type: see 5G vs fibre and LTE vs fibre, where fibre’s low, stable latency is its biggest edge.
Want low, stable latency?
Fibre is the most consistent connection for gaming and calls. Check what’s available at your address.