Coverage maps are predictions, usually for outdoors, and they disagree because operators use different methods. Check each network's own checker for 5G and standalone, compare with Ofcom's independent checker, then test on site. On the device, signal quality (SINR) tells you more than signal strength (RSRP), and the best spot for a router is often a window or an external antenna rather than the room you want internet in.
Every coverage map I have ever used has been right somewhere and wrong somewhere else. That is not a criticism. They are computer predictions based on mast positions, terrain and assumptions about buildings. They are a good place to start and a bad place to finish.
Step 1: check each network’s own map
EE, O2 and VodafoneThree all have postcode checkers, and they now show standalone separately from ordinary 5G (as 5G+ or 5G Ultra). Check all three, not just the one you are with. Note whether the prediction is for outdoors or indoors. Most headline 5G figures are outdoor.
Step 2: compare with Ofcom
Ofcom runs an independent mobile coverage checker built from operator data using a common method. It is useful as a sanity check because it applies the same rules to every network. Ofcom also reports at different confidence levels for 5G, which is a reminder that a coloured map is a probability, not a promise.
Step 3: test where the device will actually live
A phone test in the car park says little about a router in a basement plant room. Test at the intended location, and at the best candidate spot for an antenna. If you can, test all three networks. A cheap pay-as-you-go SIM for each is a small price for getting the decision right.
Reading the numbers
Routers and field test menus show three main values for 5G (sometimes with “SS” in front, for synchronisation signal):
| Measure | What it tells you | Excellent | Good | Fair | Poor |
|---|---|---|---|---|---|
| RSRP (dBm) | Signal strength | above -80 | -80 to -90 | -90 to -100 | below -100 |
| RSRQ (dB) | Signal quality including load | above -10 | -10 to -15 | -15 to -20 | below -20 |
| SINR (dB) | Signal against noise and interference | above 20 | 13 to 20 | 0 to 13 | below 0 |
These are rules of thumb, not standards, but they work. If you only look at one number, make it SINR. A strong signal with high interference is worse than a modest signal that is clean.
Is it standalone?
Coverage for standalone and coverage you can use on standalone are different things: your SIM, plan and device all have to allow it. The standalone guide explains how to confirm what a phone or router is actually connected to.
Antennas and placement
- Height and windows first. Moving a router from a desk to a high, outward-facing window often beats any accessory.
- External antennas transform marginal sites. Make sure they cover 3.4 to 3.8 GHz for 5G capacity, not just older 4G bands.
- Cable loss is real, and worse at higher frequencies. Keep runs short and use decent low-loss cable, or mount the router outdoors and run Ethernet instead. See outdoor 5G routers.
- MIMO needs all its ports. A 4×4 router with two antennas connected is leaving performance behind.
Questions people ask
Why does the map say 5G but I only get 4G indoors?
Coverage maps mostly predict outdoor signal. 5G at 3.5 GHz loses a lot of strength through walls and modern insulated glass, so indoor coverage can be far weaker than the map suggests.
What is a good SINR for 5G?
As a rough guide, above 20 dB is excellent, 13 to 20 dB good, 0 to 13 dB usable, and below 0 dB poor. SINR is usually the best single predictor of real speed.
Will an external antenna help 5G?
Often a great deal, particularly where the router is indoors or the mast is distant. Make sure the antenna covers the 5G bands in use, especially 3.4 to 3.8 GHz, and use short, good quality cable.