This guide answers one question for Guildford: which mobile network gives the best signal, and where the answer changes. Every figure in it comes from the same May 2025 coverage measurements behind NetScan's Guildford coverage checker, based on 1,569 addresses in 99 sampled postcodes across 18 postcode districts (GU1 to GU20). Nothing here is estimated, and no network is called best where the data does not say so.
Across Guildford as a whole, no network wins on coverage: the overall scores are EE 100, O2 99, Three 98, Vodafone 98 out of 100, a spread of 2 points, which is too close to call a winner. Outdoors they are level: across the four, good outdoor 4G reaches 100% of sampled addresses and the top 'enhanced' outdoor grade 99-100%. Indoors they are not: good indoor signal ranges from 90% of addresses (Three) to 99% (EE).
The real differences are local. In 6 of the 18 districts, at least one network's indoor figure sits 5 or more points behind the others, and the gap can be large: in GU6, 0% of the 116 addresses sampled get good indoor Three signal. This guide maps those districts, so you can see whether yours is one of them before you pick a network.
Guildford at a glance: the four networks side by side
These are the Guildford-wide figures, pooled across all 18 districts and weighted by the number of addresses sampled in each. They are the same numbers the Guildford coverage checker shows. The order is the checker's (overall score, ties broken alphabetically); it is not a recommendation.
What the columns mean: Each sampled address is graded for its predicted signal. '5G-grade outdoor' is the share of addresses at the top 'enhanced' outdoor data grade, a signal-strength grade rather than a promise of 5G service on your plan. 'Good outdoor 4G' is the share with good or better outdoor data signal, and 'Good indoor' the share with good or better indoor data signal. 'Overall' blends the three (35%, 50% and 15%).
| Network | Overall | 5G-grade outdoor | Good outdoor 4G | Good indoor |
|---|---|---|---|---|
| EE | 100/100 | 100% | 100% | 99% |
| O2 | 99/100 | 100% | 100% | 94% |
| Three | 98/100 | 100% | 100% | 90% |
| Vodafone | 98/100 | 99% | 100% | 92% |
Based on 1,569 addresses in 99 postcodes, GU1 to GU20 (May 2025 data).
Where the networks differ in Guildford: district by district
The Guildford-wide averages hide the districts where one network falls behind indoors. The table lists every district where the four networks' good-indoor figures are 5 or more points apart. The lowest readings are Three in GU6 (0% of 116 addresses), Vodafone in GU6 (11% of 116 addresses), O2 in GU6 (45% of 116 addresses) and O2 in GU5 (55% of 53 addresses).
It is not the same network everywhere. Trailing by 5 or more points indoors: O2 in GU5, GU6 and GU18; Three in GU6, GU9 and GU20; Vodafone in GU5, GU6 and GU8; EE in GU5. That is why a single 'best network in Guildford' answer does not hold up, and why the district you live or work in matters more than the city.
Outdoor signal differs in fewer places: in GU5, Vodafone reaches the 5G-grade level at 85%. Everywhere else in the table the four are level outdoors and differ only indoors.
| District | Addresses | EE | O2 | Three | Vodafone |
|---|---|---|---|---|---|
| GU5 | 53 | 89% | 55% | 94% | 72% |
| GU6 | 116 | 100% | 45% | 0% | 11% |
| GU8 | 55 | 100% | 100% | 100% | 93% |
| GU9 | 69 | 100% | 100% | 64% | 100% |
| GU18 | 132 | 100% | 95% | 100% | 100% |
| GU20 | 51 | 100% | 100% | 78% | 100% |
Good indoor data signal, share of sampled addresses. May 2025 data.
The Guildford districts where all four measure the same
In 8 of the 18 districts (GU2, GU7, GU11, GU12, GU14, GU16, GU17 and GU19) the figures are identical for EE, O2, Three and Vodafone on all three measures: 5G-grade outdoor, good outdoor 4G and good indoor. If your address is in one of these, the coverage data gives you no reason to prefer one network, so the useful comparison is plan price, contract length and roaming, including the cheaper SIM brands that share each network's masts.
Choosing a network in Guildford with this data
Start with your district rather than the city. If it is in the table above, look at which network trails there and treat that as the one to check hardest, especially if you use your phone mostly indoors. A figure of 0% means none of the 116 addresses sampled in GU6 is predicted good indoor Three signal; a sample is not every address, so check your own postcode.
If your district is not in the table, the four networks measure within 5 points of each other indoors there and are level outdoors, so the decision moves to price and terms. Either way, the network you choose also decides which SIM brands you can use on it: giffgaff and Tesco Mobile run on O2's masts; SMARTY and iD Mobile on Three's; VOXI, Talkmobile and Lebara on Vodafone's; and 1pMobile on EE's. A SIM brand gets its host network's coverage, so the district figures above apply to it as well. Plan prices change often, so check the provider's own site for today's price.
What these figures can and can't tell you
The data is a prediction of signal at each sampled address, not a speed test, and the sample per district ranges from 16 to 181 addresses in Guildford. Indoor signal in particular depends on the building: thick walls, basements and foil-backed insulation all cut it. The figures cover the 18 districts from GU1 to GU20 that NetScan holds measurements for.
Two practical checks close the gap. Run your full postcode through NetScan's scanner to see the four networks for your own district, then confirm on the operator's own coverage checker. If indoor signal is the problem at home, Wi-Fi calling on a compatible phone and plan routes calls over your broadband instead.