What a connection is worth in real data, what speed your household actually needs, and what a website will cost you in transfer — with megabits and megabytes kept straight throughout.
Connection speed
Drop this to 90% for a realistic sustained figure once protocol overhead is taken off, or lower still on busy shared links.
How fast do I need to be?
The provisioning question in reverse — move this much, inside this window.
Your plan
Mbit/s
Happening at the same time
How many of each at the busiest moment — a weeknight, usually.
Monthly data
Traffic
Page weight is everything the browser pulls — HTML, CSS, JavaScript, fonts and images. Your browser’s network tab reports it per page.
Traffic is never flat. A typical site sees 10–15% of its daily total in its busiest hour; a news or launch spike can be far higher.
Units
Throughput
—
In megabits—
In bytes per second—
Per minute—
Per hour—
Per day—
Per 30-day month—
Per year, flat out—
To move that volume in that window
—
Raw requirement—
Provision at least—
At the speed above it would take—
Speed you need
—
—
Before headroom—
Plan to look for—
Where it goes
Data used
Per day—
Per 30-day month—
Against your cap—
Remaining—
Transfer
—
Per day—
From your origin—
Average throughput—
Busiest hour—
Peak at the origin—
Request rate—
Port speed that covers the peak—
Hosts that bill on the 95th percentile charge against your busiest sustained five minutes, not your monthly total — so the peak row is the one that decides the bill.
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Bandwidth, throughput and speed are three things
Bandwidth is capacity — the maximum a link can carry, which is what an ISP sells you. Throughput is what you actually get once protocol overhead, congestion and the far end’s limits have taken their cut, typically 85–95% of the headline figure on a wired connection. Latency is delay, and it is unrelated to both: a satellite link can have generous bandwidth and still feel slow because every packet takes 600 ms to make the round trip.
This matters when you are diagnosing a complaint. Video calls stuttering on a 500 Mbit/s line is almost never a bandwidth problem — a call needs about 3 Mbit/s. It is jitter, packet loss, or Wi-Fi. Buying more bandwidth fixes nothing.
The factor of eight
Connections are sold in megabits per second; files are measured in megabytes. There are eight bits in a byte, so a 100 Mbit/s line moves at most about 12.5 MB/s. Watch the case: Mb is megabits, MB is megabytes. Nearly every “my internet is slower than advertised” complaint is this conversion, not a fault.
Decimal or binary
Network rates are always decimal — 1 Mbit/s is exactly 1,000,000 bits per second. File sizes are ambiguous: Windows reports binary megabytes of 1,048,576 bytes, while storage makers, macOS and most bandwidth billing use decimal ones of 1,000,000. The gap is about 5% per unit step and roughly 10% by the terabyte, which is why a 1 TB drive shows up as 931 GB. Switch the toggle to match whatever showed you the number.
Why household speeds do not simply add up
The calculator sums the activities running at once, then adds headroom, because that is the honest worst case — but real households rarely hit it. Streaming services use adaptive bitrates and back off when the link is busy, buffers absorb short spikes, and nobody starts four 4K films at the same instant. Treat the total as the point at which things start competing rather than a hard requirement.
Two things do deserve extra room. Uploads are usually a fraction of download speed on cable and DSL, so a cloud backup or a live stream can saturate the up-link while the down-link sits idle. And a single old device on 2.4 GHz Wi-Fi can drag a whole access point down regardless of what the line outside is capable of.
The per-activity figures above are sustained averages rather than the “recommended minimum” numbers streaming services publish, because minimums are padded for safety and make planning figures look worse than reality. A 4K stream averages around 16 Mbit/s, which works out at roughly 7 GB an hour. A 1080p stream is about 6 Mbit/s and 2.7 GB an hour, and an SD stream is nearer 1 GB an hour.
The surprises run in both directions. Online gaming is remarkably light during play — about 1 Mbit/s, or under half a gigabyte an hour — because only game state travels, not video. It is the downloads that hurt: a 100 GB title is a fortnight of streaming in one sitting. Music is trivial at 0.32 Mbit/s even at the highest quality, and a video call sits around 3 Mbit/s.
Data caps and the monthly picture
Convert once and the cap stops being mysterious: 1 Mbit/s running flat out for a month moves about 324 GB. So a 1.2 TB cap, the common US figure, is roughly 3.7 Mbit/s sustained around the clock — generous for browsing, tight for a household that watches several hours of 4K a day. Four hours a day of the default mix here comes to just under 2 TB a month.
Sizing a website or server
Monthly transfer is pageviews multiplied by page weight, and page weight is everything the browser fetches — HTML, CSS, JavaScript, fonts and images. The median page is now well over 2 MB, so 250,000 pageviews a month is around 550 GB. The average throughput that implies is tiny, under 2 Mbit/s, which is exactly why average figures mislead.
Traffic arrives in a lump. If 12% of a day’s visits land in the busiest hour, peak demand is several times the average, and many providers bill on the 95th percentile — your busiest sustained five-minute window across the month, with the top 5% discarded. Under that model the peak decides the bill, not the total. A CDN changes the arithmetic entirely by serving static files from its own edge, cutting origin transfer by the offload percentage while leaving the visitor-facing total unchanged.
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Frequently asked questions
How much internet speed does a family of four need?
Add up what runs at the same time. A typical weeknight — one 4K stream, a couple of HD streams, a video call, someone gaming and two people browsing — comes to roughly 45 Mbit/s with headroom. A 100 Mbit/s plan covers that comfortably; anything above 300 Mbit/s is bought for download speed and future-proofing rather than concurrency.
How many GB does 4K streaming use per hour?
About 7 GB an hour at a typical 16 Mbit/s average bitrate. HD at 1080p is closer to 2.7 GB an hour and SD around 1 GB. A two-hour film in 4K is therefore roughly 14 GB, so a 1.2 TB monthly cap allows about 85 of them before anything else is counted.
Is 100 Mbps enough?
For almost every household, yes. It carries four simultaneous 4K streams with room left over. Where 100 Mbit/s starts to strain is large downloads — a 100 GB game takes about two and a quarter hours — and uploads, since 100 Mbit/s plans on cable often pair with 10 Mbit/s or less going out.
What is the difference between bandwidth and speed?
Bandwidth is the capacity of the link, speed is how fast a given transfer actually moves, and the second is limited by more than the first. A single download can be capped by the server, by disk write speed or by distance and latency long before it uses the bandwidth available.
How do I convert Mbps to MB/s?
Divide by eight. 100 Mbit/s is 12.5 MB/s, 500 Mbit/s is 62.5 MB/s and 1 Gbit/s is 125 MB/s. Going the other way, multiply by eight. The distinction is the lower-case b for bits against the upper-case B for bytes.
How much bandwidth does a website need?
Multiply monthly pageviews by average page weight, then size for the peak rather than the average. A site with 250,000 monthly pageviews at 2.2 MB a page moves 550 GB, which averages under 2 Mbit/s but peaks near 5 Mbit/s in its busiest hour. Putting static assets behind a CDN cuts origin transfer in direct proportion to the share it serves.