How to check 5G coverage properly
Coverage maps are a starting point, not a guarantee. Every major UK operator publishes a coverage checker on their website. Enter your postcode or address and the map shows indoor and outdoor 5G coverage, typically split by band or by use case (voice, data, 5G).
The limitations of these maps are important to understand. They are generated from propagation models, not from actual measurements. They show predicted signal levels at average building stock, not at your specific property. Hills, dense vegetation, building construction materials, and local obstructions all affect reality versus the model.
The independent tools
For a more detailed view, Mastdata provides an independent 5G coverage layer that aggregates crowd-sourced signal data alongside official operator information. Ofcom’s Connected Nations report publishes annual coverage data that can be cross-referenced with operator claims.
For specific site assessment, the most reliable approach is a physical test: put a compatible SIM from your target operator into a 5G phone, hold it in the location where your CPE would sit, enable field test mode, and read the actual signal levels and band indicators. This takes 30 minutes and costs the price of a pay-as-you-go SIM.
Understanding signal metrics
Two key signal quality metrics appear in phone field test modes and router diagnostic interfaces:
RSRP (Reference Signal Received Power) measures signal strength in dBm. A value above -80 dBm is strong. -80 to -100 dBm is usable. Below -100 dBm is marginal and below -110 dBm is very poor for FWA use. Note that these thresholds apply differently to different frequency bands.
SINR (Signal to Interference plus Noise Ratio) measures signal quality relative to interference. Above 10 dB is good. 0-10 dB is moderate. Below 0 dB indicates significant interference and poor performance regardless of raw signal strength.
What marginal coverage means in practice
If you are shown as marginally covered on operator maps, or if your SIM test shows RSRP in the -95 to -105 dBm range, an outdoor CPE or external directional antenna will typically improve performance to usable levels. The 10-20 dB gain from moving an antenna outside the building fabric often makes the difference between an unusable and a functional connection.
If your SIM test shows no 5G signal at all and 4G is also weak, neither indoor nor outdoor 5G hardware will solve the problem. A satellite broadband service (Starlink or equivalent) may be the better option for genuinely uncovered properties.