What Internet Speed Do I Need for Business VoIP?

Most businesses ask "what internet speed for VoIP" expecting a big number. The honest answer is that almost any modern connection has the headroom — what wrecks call quality is congestion, jitter and asymmetric upload, not a low Mbps figure. This guide gives the real numbers, the thresholds that matter, and when to move from broadband to a leased line. It sits under our business VoIP pillar, where you can see how the whole phone system fits together.

How much bandwidth does a single VoIP call actually use?

A single VoIP call uses roughly 85–100 Kbps in each direction on the G.711 codec, or about 30 Kbps on the more compressed G.729 codec. That is a fraction of any business connection. For a 20-person office with up to 10 simultaneous calls, you need around 1 Mbps reserved for voice — trivial against typical UK broadband.

Ofcom's Connected Nations 2024 report puts the average UK broadband download speed at 69.4 Mbps, so raw bandwidth is almost never the bottleneck for voice (Ofcom). The number that breaks calls is not Mbps — it is how cleanly each small voice packet arrives.

Why do latency and jitter matter more than raw speed?

Voice is real-time, so timing beats volume. VoIP needs one-way latency below roughly 150ms and jitter below about 30ms for clean calls. Past those thresholds you hear delay, talk-over and robotic, choppy audio — even on a fast line that looks healthy in a speed test.

• Latency — the delay between speaking and being heard. High latency causes that awkward "you go… no, you go" overlap.
• Jitter — variation in packet arrival time. High jitter scrambles the order voice packets play back in, causing gaps and warble.
• Packet loss — dropped packets the codec cannot rebuild, heard as clipped words.

A speed test cannot see any of this. That is why a 900 Mbps shared broadband line can sound worse than a modest, well-managed connection: the shared line spikes in latency and jitter under load, and voice is the first thing to suffer.

How much total internet speed does my business need for VoIP?

Size your connection by concurrent calls, not headcount. Most offices peak at far fewer simultaneous calls than people. Multiply your busiest-hour concurrent calls by about 100 Kbps for voice, then leave generous room for everything else on the line — email, cloud apps, backups and video.

Bandwidth figures assume roughly 100 Kbps per concurrent call and exclude other traffic. The takeaway: the voice requirement is tiny, so the real decision is connection *quality* and *symmetry*, not picking a bigger speed tier. For multiple sites, our multi-site VoIP approach keeps quality consistent across every location.

Why is upload speed critical for VoIP call quality?

VoIP sends voice in both directions, so upload matters as much as download. Standard broadband is asymmetric — upload is often a fraction of download — and when a cloud backup or large file transfer saturates that upload, call quality collapses while your download still looks fine.

This is the single most common cause of "our internet is fast but calls keep breaking up." A symmetrical connection such as a leased line gives upload equal to download, so voice has reliable headroom regardless of what else is uploading. If you are weighing the options, our guide to what a leased line is explains the symmetry difference in plain terms.

Do I need a leased line or will business broadband do?

For most small offices with light call volumes, FTTP or fibre broadband with QoS is fine. Once you have heavy concurrent call volumes, multiple sites, or calls that directly drive revenue, a leased line becomes the right call — it is uncontended, symmetrical, and comes with a guaranteed service level.

• Choose broadband when: under ~10 concurrent calls, single site, occasional file transfers.
• Choose a leased line when: consistent high call volumes, contact-centre or sales-floor usage, multi-site voice, or zero tolerance for downtime.

A leased line is typically backed by a 99.99% uptime SLA and can carry carrier-level QoS so voice packets are prioritised across the network, not just inside your office. For larger estates, SD-WAN can blend multiple links and steer voice onto the cleanest path automatically.

What is QoS and does my router need it for VoIP?

Quality of Service (QoS) is a network setting that prioritises voice traffic over less time-sensitive data like downloads, backups and web browsing. Without it, one large upload can starve your calls of capacity for a few critical seconds, and you hear it instantly as broken audio.

On business broadband, QoS lives in your router and only controls your own LAN. On a leased line, QoS can be enforced at the carrier level, so voice packets keep priority across the whole path. If voice runs through Microsoft Teams or a hosted phone system, getting QoS right is what separates "usable" from "boardroom-grade."

How does the PSTN switch-off change my VoIP bandwidth planning?

The UK's analogue phone network (PSTN) is being retired, with the industry switch-off scheduled for 31 January 2027 — every business line must move to VoIP before then (Ofcom). That makes connection quality a board-level issue, not an IT detail, because your phones now depend entirely on your internet.

Industry figures suggest the majority of UK landlines have already migrated to digital voice (industry data, 2026), and adoption is accelerating. Plan the move early: audit your upload, confirm QoS, and decide broadband-versus-leased-line before you are forced to. Our PSTN switch-off guide walks through the deadline and the migration steps.

What about security once your phones run over the internet?

When voice runs over your data network, it inherits your network's risk: toll fraud, call interception and denial-of-service all become possibilities. Securing the connection is now part of securing the phone system, which is why we treat VoIP and security as one job, not two.

Good practice — strong SIP credentials, encryption, segmentation and monitoring — keeps voice traffic protected. The NCSC publishes practical guidance on securing business communications and networks (NCSC). For the specifics of locking down hosted voice, see our VoIP security guidance.