The Short Version
Sub-6 5G means 5G below 6 GHz. It includes low-band and mid-band 5G, and it is what most people use most of the time. mmWave 5G uses much higher frequencies, usually above 24 GHz. It can be incredibly fast, but it covers tiny areas and struggles through walls, windows, trees, and even your hand.
mmWave vs Sub-6 at a Glance
| Feature | Sub-6 5G | mmWave 5G |
|---|---|---|
| Frequency range | Below 6 GHz | 24–100 GHz |
| Coverage | Wide to medium | Very short range (100–200 m) |
| Indoor use | Good to usable | Usually zero signal indoors |
| Typical peak speed | 300–900 Mbps (mid-band) | 1–4 Gbps (ideal outdoor) |
| Main advantage | Coverage and reliability | Capacity and peak speed |
The Physics of mmWave
mmWave uses frequencies between roughly 24 GHz and 100 GHz, where radio wavelengths are measured in millimeters — hence the name. At these frequencies, physics works against coverage in several ways. Oxygen molecules absorb energy at 60 GHz, causing additional signal loss over distance. Glass reflects mmWave rather than passing it through, so a window blocks much of the signal instead of letting it in. Leaves, walls, and even a hand placed over the phone's antenna can attenuate the signal by 20–40 dB — enough to drop connection entirely. Diffraction, which allows lower-frequency signals to bend around corners and obstacles, is extremely limited at millimeter wavelengths, making mmWave essentially a line-of-sight technology outdoors.
mmWave Infrastructure Requirements
Because mmWave cells cover only 100–200 meters in good conditions, continuous coverage requires small cells placed every block. In practice, Verizon's Ultra Wideband mmWave deployment — the most extensive in the US — is concentrated in dense downtown blocks of major cities, major airports, and sports stadiums. Even within those footprints, stepping indoors typically drops mmWave coverage to zero. Deploying enough small cells for neighborhood-level mmWave coverage would require hundreds of thousands of installations nationwide and an enormous ongoing maintenance cost, which is why no carrier has attempted it.
Real mmWave Throughput
In ideal outdoor conditions with a clear line of sight to a small cell and minimal congestion, mmWave 5G can deliver 1–4 Gbps peak download speeds. Under typical good outdoor conditions — standing still near a cell, clear weather, moderate device load — 1 Gbps is a realistic expectation. Indoors, or more than 200 meters from a cell, the practical throughput is essentially zero as the phone falls back to sub-6 or LTE. Speed test records from mmWave almost always come from near-ideal conditions that do not represent everyday use.
Sub-6 GHz: The Taxonomy That Matters
Sub-6 GHz 5G is not a single thing — it spans a wide range of frequencies with very different performance profiles:
- Low-band (600–850 MHz): Excellent coverage reaching miles from a tower, penetrates buildings well, but delivers only 50–150 Mbps peak — not dramatically faster than LTE in practice. T-Mobile's n71 (600 MHz) and AT&T's n14 (758 MHz) fall here.
- Mid-band (2.5–4.2 GHz): The practical sweet spot for 5G. Covers neighborhoods and reaches inside many buildings while delivering 300–900 Mbps peak. T-Mobile's n41 (2.5 GHz) — acquired from Sprint — is the prime example, and it drives most of T-Mobile's speed advantage in 2025.
- C-band (3.7–3.98 GHz): The frequencies auctioned by the FCC in 2021 for $81 billion. AT&T and Verizon's primary mid-band investment. Similar coverage to 2.5 GHz with strong capacity. Peak speeds of 400–900 Mbps in well-deployed areas.
Carrier Speed Comparison by 5G Tier
| Carrier / Band | Type | Typical Download | Coverage |
|---|---|---|---|
| T-Mobile n71 (600 MHz) | Low-band | 50–150 Mbps | Nationwide including rural |
| T-Mobile n41 (2.5 GHz) | Mid-band | 300–700 Mbps | Cities and suburbs |
| AT&T / Verizon C-band (3.7 GHz) | Mid-band | 400–900 Mbps | Dense urban and suburban |
| Verizon UW mmWave (28/39 GHz) | mmWave | 1,000–4,000 Mbps | Stadiums, airports, select blocks |
Why Your 5G Icon Does Not Guarantee Speed
A 5G icon does not reveal which band you are on. Carriers display a single "5G" indicator regardless of whether you are on 50 Mbps low-band 5G or 1 Gbps mmWave. Some carriers have added labels like "5G UW" (Verizon), "5G+" (AT&T), or "5G UC" (T-Mobile) to indicate mid-band or mmWave connections, but even these vary by device. The only reliable way to know what speed your 5G connection delivers is to run a speed test or check field test mode for band information.
Which One Should You Care About?
- For normal phone use, mid-band sub-6 matters most.
- For rural coverage, low-band sub-6 matters most.
- For packed venues and dense urban blocks, mmWave can be excellent.
- For home internet via 5G, mid-band sub-6 is the only practical option — mmWave does not work indoors.
- For buying a phone, sub-6 support is essential; mmWave support is only worth prioritizing if you live or work in a dense US city where Verizon mmWave is deployed.
Frequently Asked Questions
Is mmWave 5G faster than sub-6 5G?
Yes, mmWave can be much faster because it uses very wide channels. But it works only over short distances and is easily blocked, so most people use sub-6 5G far more often.
Does every 5G phone support mmWave?
No. Many 5G phones support sub-6 only. mmWave requires extra antenna hardware and is more common in higher-end US carrier models than in budget or international models.
Which is better, mmWave or sub-6?
Neither is universally better. mmWave is best for dense outdoor areas that need huge capacity. Sub-6 is better for everyday coverage, indoor use, suburbs, roads, and rural areas.