What is a good WiFi signal strength in dBm?

Signal strength is measured in negative numbers, and closer to zero is stronger. Above -55 dBm is excellent, -55 to -70 dBm is good, -70 to -85 dBm is fair and this is where speeds start to suffer, and anything below -85 dBm is barely usable.

Why does my phone stay on a weak WiFi signal when a stronger one is available?

This is called sticky client behaviour. Your phone decides which access point to use when it first connects and is reluctant to switch afterwards, so in a mesh or extender setup it can cling to a distant node long after you have walked away from it. Turning WiFi off and on forces the phone to choose again.

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Weak WiFi signal in one room? How to fix dead spots

Everything works fine in the living room. Move to the back bedroom, the garden, or the upstairs office and pages crawl, video calls drop, and your phone quietly gives up and switches to mobile data. The internet isn't broken - the signal just isn't reaching.

This is the most common WiFi complaint there is, and also the most fixable, once you know what you're actually looking at.

What the dBm number means

Signal strength is measured in dBm, and it's always a negative number. Counter-intuitively, closer to zero is stronger: -45 dBm is a great signal, -85 dBm is nearly nothing. The rough scale:

Above -55 dBm - excellent. You're near the router with a clear path. Everything works.
-55 to -70 dBm - good. Normal for a room or two away. No problems here.
-70 to -85 dBm - fair. This is where trouble starts: slower speeds, occasional stalls, calls that break up.
Below -85 dBm - weak. Technically connected, practically unusable.

Every 3 dB is roughly a halving or doubling of signal power, so the difference between -60 and -75 is much bigger than the numbers suggest.

Why a weak signal is slower than you'd expect

Speed doesn't fall off gently as signal drops. When the connection gets marginal your device switches to slower, more robust ways of encoding data, deliberately trading speed for reliability. On top of that, packets that don't make it have to be sent again. The result is that throughput collapses much faster than the little signal-bars icon implies - going from three bars to two can easily halve your real-world speed.

This is also why a weak signal often looks like a completely different problem: the stalls and retries show up as packet loss.

How to fix it, in order of effectiveness

Move the router before you buy anything. It wants to be central, high up, and in the open. Routers get hidden in cupboards, behind televisions, and on the floor behind furniture, all of which are the worst possible places. A router moved from a cupboard in the corner to a shelf in the hallway can transform coverage for free.
Look at what's in the way. Brick, concrete and stone are the big blockers. So are mirrors, metal appliances, underfloor heating, foil-backed insulation and anything containing water - including people. One wall is fine; three walls and a chimney breast is what creates a dead spot.
Use 2.4 GHz for distance. If you're at the far end of the house, the 2.4 GHz band travels considerably further and penetrates walls better than 5 GHz. It's slower, but a slower usable connection beats a faster unusable one. See 2.4 GHz vs 5 GHz.
Add a second access point where it's actually needed. If moving the router can't cover the house, this is the real fix: a mesh system, or a wired access point on the far side. Anything connected back by cable or powerline is far better than a repeater, because it doesn't have to relay traffic over the air.
Treat plug-in extenders as a last resort. A repeater has to receive and re-transmit every packet on the same airwaves, which roughly halves throughput and adds to congestion. It can rescue a dead spot, but it will never feel like being near the router.

Where to put a mesh node: halfway between the router and the dead spot, not in the dead spot. A node that can barely hear the router has nothing good to share with your phone.

The other cause: your phone is stuck on the wrong access point

If you have a mesh system or an extender, there's a second possibility worth checking, because it looks identical from the sofa. Devices choose an access point when they first connect and are stubborn about changing afterwards - behaviour known as the "sticky client" problem. You walk from the kitchen to the bedroom, a much closer node is available, and your phone carries on talking to the one downstairs.

The giveaway is that signal is poor in a spot where another access point is physically nearer. The instant fix is to toggle WiFi off and on, which forces a fresh choice. If it happens constantly, look for band steering or fast-roaming options in your mesh app, or check the manufacturer's documentation, and verify that all nodes share the same network name and password.

What doesn't fix it

Upgrading your internet plan changes nothing - the bottleneck is the last few metres of air between your device and the router, not the line into your home. Nor does a newer phone; Wi-Fi 6 and 7 improve efficiency in busy environments, but they can't manufacture signal that isn't there. And if the connection is strong but still slow, the problem is elsewhere: check channel congestion or bufferbloat instead.

The WiFi Doctor in the ClearWiFi Android app shows live signal strength in dBm with a plain-language rating, warns you when it drops into the range where speeds suffer, and spots when you're stuck on a distant access point while a stronger one is in range. No ads, no tracking, no subscription. Get it on Google Play.