Bandwidth Calculator

About the Bandwidth Calculator

Three bandwidth jobs on one page. Speed and data turns a sustained speed into the data it moves in an hour, a day, a month or a year (100 Mbit/s flat out is 45 GB an hour and 32.4 TB in a 30-day month), or an amount of data into the average speed it needs (1 TB a month is 3.09 Mbit/s around the clock). Website hosting sizes a site’s monthly transfer from its page weight and page views, with the speed of the busiest hour, the share a CDN serves and a margin for growth. Home or office adds up streaming, video calls, music, live streams and downloads from the figures Netflix, YouTube, Zoom and Spotify publish, to show the data a month and the speed everything needs at once, so you can choose a plan or a data cap.

Every figure comes with its working. Without a pass you see a free preview: the monthly data (or the speed you solve for) in full, with the first rows of each table and the first step of the working; Copy result and the CSV unlock with a Pro pass.

Common uses

• Choosing between internet plans by speed and by monthly data allowance.
• Checking whether a data cap covers a family’s streaming, school or work video calls and game downloads.
• Sizing the monthly transfer of a hosting plan or a CDN before a launch, a sale or a campaign.
• Working out what a backup, a sync or a live stream will need from a connection.

Bits, bytes and the two kinds of gigabyte

Speeds are counted in bits a second with decimal prefixes: 1 Mbit/s is 1,000,000 bits a second, and a byte is 8 bits, so 100 Mbit/s moves 12.5 MB a second. Data is counted in bytes: a gigabyte (GB) is 10⁹ bytes. The binary prefixes (first set in IEC 60027-2, now part of IEC 80000-13) count in powers of 1,024 instead: a gibibyte (GiB) is 2³⁰ = 1,073,741,824 bytes, about 7% more than a GB, and a TiB about 10% more than a TB (NIST: prefixes for binary multiples). Some software writes binary amounts with the decimal symbols, which is why the same file can read 1 GB in one place and 1.07 GB in another; this page shows both.

Where the service figures come from

Each activity uses the figures its service publishes:

• Netflix: 3 Mbit/s for HD 720p, 5 Mbit/s for Full HD 1080p and 15 Mbit/s for 4K (internet connection speed recommendations), and up to 0.3 GB an hour on Low, 0.7 GB on Medium, and on High up to 1 GB (SD), 3 GB (HD) and 7 GB (4K) per device (how much data Netflix uses). Its data per hour is used as published; for Low, Medium and SD, which have no published speed, the speed is the average rate of that data.
• YouTube: recommended sustained speeds of 0.7 Mbit/s for 360p, 1.1 for 480p, 2.5 for 720p, 5 for 1080p and 20 for 4K (system requirements); live streams use the recommended H.264 bitrate settings: 8 Mbit/s for 720p, 14 for 1080p at 30 fps and 17 at 60 fps, 21 and 34 for 1440p, 42 and 50 for 4K, all upload (live encoder settings).
• Zoom: 600 kbit/s each way for a 1:1 call in high quality, 1.2 Mbit/s for 720p and 3.8 up / 3.0 down for 1080p; group calls 1.0 up / 0.6 down, 2.6 / 1.8 for 720p and 3.8 / 3.0 for 1080p; audio 60–80 kbit/s, counted here as 80 each way (system requirements).
• Spotify: about 24, 96, 160 and 320 kbit/s for Low, Normal, High and Very high (audio quality).

Where a service publishes only a speed, an hour of it is worked out as that speed for the whole hour: Mbit/s × 3,600 ÷ 8 = MB. Recommended speeds leave room to spare, so this is an upper estimate of the data.

How hosting bandwidth is estimated

Monthly transfer = average page weight × page views (+ any other transfer) × (1 + margin). The average speed spreads that over the month: transfer × 8 ÷ (days × 86,400 s). Traffic is not even, so the speed of the busiest hour is the average × your peak factor: the busiest hour’s page views ÷ an average hour’s, which your analytics show hour by hour. A CDN or cache serves part of the transfer, so your own server sends only the rest. Hosting plans state the monthly transfer they include (GB or TB), the speed of the server’s connection (Mbit/s or Gbit/s), or both: compare the first with the monthly figure and the second with the busiest hour.

Choosing a plan or a data cap

Two figures matter. Data a month is what a data allowance must cover; uploads (video calls, live streams, backups) count towards it if your plan counts both directions, so check its terms. Speed at once is what everything listed needs when it all runs at the same time; download and upload are separate figures, and plans list their speeds separately too, so compare both. Add a margin for Wi-Fi, other devices and background updates if you like: it is your own choice, not a published figure. To see what your connection delivers now, run the internet speed test.

Limitations

• The service figures are the speeds the services recommend and, for Netflix, the most data an hour can use (“up to”); what a title, device or network really uses varies. Your router’s or your provider’s usage meter shows what your home actually uses.
• It calculates; it does not measure your connection. The internet speed test does.
• The page weight, peak factor and CDN share are your own estimates; the results are only as good as they are.
• Protocol overhead (packet headers, retransmissions) is not added: a line moves a few per cent less file data than its speed. The download time calculator adds an overhead allowance.
• A month counts 30 days unless you choose an average month (30.44 days) or 31 days, and a year 365 days.

Privacy

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