"My plan is 100 megs, so why does the download say 11 MB/s?" is one of the most common questions any help desk hears. The answer — bits versus bytes, and decimal versus binary prefixes — is short, but it trips up experienced people as well, especially when one tool reports MB/s and another MiB/s.
The Bits & Bytes Explainer explains these relationships with tables that are calculated exactly from the unit definitions, plus a small interactive converter that shows any storage size or speed in bits, bytes, decimal and binary units at once. Everything is computed in your browser.
What is the Bits & Bytes Explainer?
In simple terms
It is a reference page with a calculator: a short explanation of bits and bytes, a Try it converter, a table comparing decimal and binary prefixes, a table of common network speeds in bytes per second, and a table of typical download times.
Technical background
- A bit is one binary digit, 0 or 1. A byte is 8 bits and holds 256 values (the page shows the byte
10110010= 178). - Storage and files are counted in bytes. Network speeds are counted in bits per second.
- Decimal (SI) prefixes are powers of 1000: k = 10³, M = 10⁶, G = 10⁹, T = 10¹², P = 10¹⁵.
- Binary (IEC) prefixes are powers of 1024: Ki = 2¹⁰, Mi = 2²⁰, Gi = 2³⁰, Ti = 2⁴⁰, Pi = 2⁵⁰.
The gap between the families grows with each step. The page calculates it exactly as (1024ⁿ ÷ 1000ⁿ − 1) × 100:
| SI | IEC | IEC larger by |
|---|---|---|
| kB = 1,000 B | KiB = 1,024 B | 2.4% |
| MB = 1,000,000 B | MiB = 1,048,576 B | 4.86% |
| GB = 1,000,000,000 B | GiB = 1,073,741,824 B | 7.37% |
| TB = 10¹² B | TiB = 1,099,511,627,776 B | 9.95% |
| PB = 10¹⁵ B | PiB = 1,125,899,906,842,624 B | 12.59% |
Why use the Bits & Bytes Explainer?
- Answer speed complaints with numbers: 100 Mbit/s is at most 12.5 MB/s, or 11.921 MiB/s.
- Explain capacity labels — why a "GB" in one place is 7% larger than in another.
- Set expectations for downloads and transfers with the theoretical-time tables.
- Teach the concepts to new colleagues or users with exact, reproducible tables instead of rules of thumb.
Who should use it?
Help-desk and support staff, junior admins, network engineers explaining link speeds to non-technical stakeholders, students, and anyone comparing ISP plans with download-manager readings. If you need a full conversion, the Data Storage Converter and Unit Converter go further; for actual measurements use the Internet Speed Test.
How the Bits & Bytes Explainer works
All tables and conversions are calculated in your browser from the same exact unit definitions used by the other NetTools.tech converters (rational numbers on BigInt, no floating-point drift).
- Try it. You enter a Value and pick a Unit from two groups: Storage (bit, B, kB, MB, GB, TB, PB, KiB, MiB, GiB, TiB, PiB) and Speed (bit/s, kbit/s, Mbit/s, Gbit/s, Tbit/s, B/s, kB/s, MB/s, GB/s, KiB/s, MiB/s, GiB/s). The value is converted to bits, then shown as:
- In bits and In bytes (bytes = bits ÷ 8), with up to 3 decimals;
- Decimal (SI) and Binary (IEC) in the most readable unit of each family (the largest unit that keeps the value at 1 or more), up to 3 decimals;
- for storage, As bits (SI) in Mbit; for speeds, In bits (SI) in the most readable bit/s unit. Negative values are rejected.
- Prefix table. The five SI/IEC pairs above, with byte counts and the percentage difference rounded to 2 decimals.
- Network speeds in bytes per second. For 10, 50, 100 and 300 Mbit/s and 1 and 10 Gbit/s: the rate in MB/s and MiB/s (3 decimals) and the theoretical time to move 1 GB.
- Typical downloads. Illustrative file sizes — photo 5 MB, song (MP3) 8 MB, HD movie 4 GB, 4K movie 20 GB, large game 100 GB — at 10 Mbit/s, 100 Mbit/s and 1 Gbit/s, at 100% of the line rate.
Durations are formatted like 2 h 13 min 20 s (at most three parts), seconds below one minute, and milliseconds below one second.
How to use the NetTools.tech Bits & Bytes Explainer
- Open the Bits & Bytes Explainer.
- Read Bits and bytes in one minute for the basics.
- In Try it, enter a Value (default
1) and choose a Unit (default GB). The results update immediately. - Compare the rows: bits, bytes, decimal, binary and Mbit.
- Use the Decimal (SI) vs binary (IEC) prefixes table when someone asks "is a KB 1000 or 1024?".
- Use Network speeds in bytes per second and How long do typical downloads take? to set expectations.
- Export with CSV, JSON, Copy all or Print. The export contains your Try-it result and all three tables with their assumptions.
Understanding the results
| Result | Meaning | What to look for |
|---|---|---|
| In bits | Value as bits (or bit/s) | Network-style count |
| In bytes | Bits ÷ 8 | What file sizes and download managers use |
| Decimal (SI) | Most readable 1000-based unit | Matches drive labels and ISP plans |
| Binary (IEC) | Most readable 1024-based unit | Matches RAM and many OS displays |
| As bits (SI) / In bits (SI) | Storage in Mbit, or speed in the best bit/s unit | Useful to compare a file size with a link speed |
| IEC larger by | Percentage gap per prefix step | 2.4%, 4.86%, 7.37%, 9.95%, 12.59% |
| MB/s and MiB/s columns | Maximum byte rate of a link | Real throughput is lower |
| Time for 1 GB / download times | Theoretical duration at 100% of the line rate | Never a guarantee |
Example: what 100 Mbit/s really delivers
Enter 100 and choose Mbit/s in Try it:
In bits 100,000,000 bit/s
In bytes 12,500,000 B/s
Decimal (SI) 12.5 MB/s
Binary (IEC) 11.921 MiB/s
In bits (SI) 100 Mbit/sThe speeds table agrees: 100 Mbit/s is 12.5 MB/s or 11.921 MiB/s and moves 1 GB in 1 min 20 s in theory. The download table shows a 4 GB HD movie at 5 min 20 s on 100 Mbit/s, 53 min 20 s on 10 Mbit/s and 32 s on 1 Gbit/s. A 100 GB game takes 2 h 13 min 20 s at 100 Mbit/s.
Now enter 1 GB: 8,000,000,000 bits, 1,000,000,000 bytes, Decimal 1 GB, Binary 953.674 MiB, and 8,000 Mbit.
Common use cases
- Explaining to users why a download manager shows about one-eighth of the advertised plan speed.
- Building quick reference slides or runbook tables (export to CSV).
- Checking whether a file size in MiB fits in a link-time budget expressed in Mbit/s.
- Teaching prefix families during onboarding.
- Sanity-checking numbers from monitoring tools that mix units.
Troubleshooting
My measured speed is far below the table value
The tables show 100% of the line rate. TCP/IP and TLS overhead, Wi-Fi, other devices, server limits and latency reduce real throughput. Measure with the Internet Speed Test and plan with the Bandwidth Calculator and its efficiency option.
The binary value looks wrong
Check whether you selected a decimal (MB) or binary (MiB) input unit — they differ by 4.86% at mega, more at giga and tera.
An error appears after typing a value
Negative values are rejected, and the input must be a number. A single comma is read as a decimal comma, so 1,000 means 1.0; type 1000.
Common mistakes
- Mixing Mb and MB. A factor of 8; write Mbit and MB to be safe.
- Applying 1024 to network speeds. Link speeds are decimal: 1 Gbit/s = 10⁹ bit/s.
- Reading the download table as a promise. It is illustrative and theoretical.
- Assuming "KB" always means 1024. Older software uses it that way; strictly kB is 1000 and KiB 1024.
Limitations
- The tables are theoretical: they ignore protocol overhead, latency, congestion and disk speed.
- File sizes in the download table are illustrative examples, not measurements of real files.
- Speeds are fixed to six common values; use the Bandwidth Calculator for your own numbers.
- Byte-rate units stop at GB/s and GiB/s; storage at PB and PiB.
Security & privacy
The page computes everything locally; the value you type is not sent anywhere. An anonymous usage counter (tool name and view or run, no inputs) may be sent unless your browser uses Global Privacy Control or Do Not Track. No personal data is needed.
Related tools
- Data Storage Converter — any size in every unit. Guide: Data Storage Converter guide.
- Unit Converter — data, rates, time and more. Guide: Unit Converter guide.
- Bandwidth Calculator — your own transfer times and required bandwidth. Guide: Bandwidth Calculator guide.
- Internet Speed Test — measure real throughput. Guide: Internet speed test guide.
- Category overview: Conversion & calculation tools.
Summary
A byte is 8 bits, storage is counted in bytes and networks in bits per second, and SI prefixes are powers of 1000 while IEC prefixes are powers of 1024. The Bits & Bytes Explainer turns those rules into exact tables and a converter, so 100 Mbit/s = 12.5 MB/s = 11.921 MiB/s is a lookup rather than a guess. Its download times are theoretical maxima.
Frequently asked questions
Why are bits written b and bytes B?
By convention a lowercase b means bit and an uppercase B means byte, so Mb is megabit and MB is megabyte. Writing Mbit and MB avoids the confusion entirely, which is the style NetTools.tech uses.
Is 1 Gbit/s Ethernet 1 GB per second?
No. 1 Gbit/s is at most 125 MB/s, because 1,000,000,000 bits divided by 8 is 125,000,000 bytes per second. Ethernet framing, IP and TCP headers reduce the usable rate a little further.
Where did binary prefixes come from?
Computer memory comes in powers of two, so kilo was long used loosely for 1024. The IEC standardized kibi (Ki), mebi (Mi), gibi (Gi) and the larger prefixes so that the SI prefixes could keep their decimal meaning.
Do network speeds use 1000 or 1024?
Network speeds use decimal prefixes: 1 Mbit/s is 1,000,000 bits per second. Binary units appear only when software reports throughput in MiB/s, which is why 100 Mbit/s is 12.5 MB/s but only about 11.92 MiB/s.
Why does a 100 Mbit/s connection download a 1 GB file in more than 80 seconds?
80 seconds is the theoretical time at the full line rate. Protocol overhead, Wi-Fi, other traffic, server limits and TCP behavior on long paths all reduce real throughput, so measured times are longer.
How many values can a byte hold?
A byte has 8 bits, so it can hold 2⁸ = 256 different values, from 0 to 255 unsigned. That is why IPv4 octets and many protocol fields range from 0 to 255.