This guide answers one question for Portsmouth: 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 Portsmouth coverage checker, based on 1,788 addresses in 107 sampled postcodes across 20 postcode districts (PO1 to PO20). Nothing here is estimated, and no network is called best where the data does not say so.
Across Portsmouth as a whole, no network wins on coverage: the overall scores are O2 100, Three 100, Vodafone 100, EE 99 out of 100, a spread of 1 point, which is too close to call a winner. Outdoors they are level: all four reach good outdoor 4G and the top 'enhanced' outdoor grade at 100% of the addresses sampled. Indoors they are not: good indoor signal ranges from 91% of addresses (EE) to 99% (Vodafone).
The real differences are local. In 6 of the 20 districts, at least one network's indoor figure sits 5 or more points behind the others, and the gap can be large: in PO17, 28% of the 47 addresses sampled get good indoor EE signal. This guide maps those districts, so you can see whether yours is one of them before you pick a network.
Portsmouth at a glance: the four networks side by side
These are the Portsmouth-wide figures, pooled across all 20 districts and weighted by the number of addresses sampled in each. They are the same numbers the Portsmouth 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 |
|---|---|---|---|---|
| O2 | 100/100 | 100% | 100% | 98% |
| Three | 100/100 | 100% | 100% | 98% |
| Vodafone | 100/100 | 100% | 100% | 99% |
| EE | 99/100 | 100% | 100% | 91% |
Based on 1,788 addresses in 107 postcodes, PO1 to PO20 (May 2025 data).
Where the networks differ in Portsmouth: district by district
The Portsmouth-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 EE in PO17 (28% of 47 addresses), EE in PO7 (32% of 85 addresses), EE in PO18 (47% of 47 addresses) and Vodafone in PO18 (72% of 47 addresses).
It is not the same network everywhere. Trailing by 5 or more points indoors: EE in PO7, PO8, PO17, PO18 and PO20; O2 in PO8, PO18 and PO20; Three in PO14 and PO20; Vodafone in PO18. That is why a single 'best network in Portsmouth' answer does not hold up, and why the district you live or work in matters more than the city.
In every one of these districts all four networks are level outdoors; the difference is indoor signal only.
| District | Addresses | EE | O2 | Three | Vodafone |
|---|---|---|---|---|---|
| PO7 | 85 | 32% | 99% | 100% | 100% |
| PO8 | 113 | 73% | 81% | 100% | 100% |
| PO14 | 76 | 100% | 100% | 83% | 100% |
| PO17 | 47 | 28% | 100% | 100% | 100% |
| PO18 | 47 | 47% | 81% | 94% | 72% |
| PO20 | 84 | 86% | 94% | 83% | 100% |
Good indoor data signal, share of sampled addresses. May 2025 data.
The Portsmouth districts where all four measure the same
In 12 of the 20 districts (PO1, PO2, PO3, PO4, PO5, PO6, PO9, PO10, PO12, PO13, PO15 and PO16) 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 Portsmouth 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 like 28% means most sampled addresses in PO17 are not predicted good indoor EE signal; it does not mean yours is one of them, 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 18 to 184 addresses in Portsmouth. Indoor signal in particular depends on the building: thick walls, basements and foil-backed insulation all cut it. The figures cover the 20 districts from PO1 to PO20 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.