File Size Calculator
Enter a file size and its unit, plus your connection speed. The calculator converts the size into every common unit and tells you how long the transfer will take.
- Decimal and binary units
- Bits and bytes
- Transfer time
Transfer times are ideal. Real downloads often reach 80% to 90% of the advertised speed.
The same file can show three different sizes. A drive maker says 1 GB is 1,000,000,000 bytes. Windows counts in powers of 1,024 and shows that file as 0.93 GB. Your internet speed is in bits, not bytes, so it looks eight times bigger. Converting between them is where most confusion comes from.
File size unit chart
Decimal and binary units side by side. Search for a unit.
| Unit | Symbol | Bytes | Type |
|---|---|---|---|
| Kilobyte | KB | 1,000 | Decimal |
| Kibibyte | KiB | 1,024 | Binary |
| Megabyte | MB | 1,000,000 | Decimal |
| Mebibyte | MiB | 1,048,576 | Binary |
| Gigabyte | GB | 1,000,000,000 | Decimal |
| Gibibyte | GiB | 1,073,741,824 | Binary |
| Terabyte | TB | 1,000,000,000,000 | Decimal |
| Tebibyte | TiB | 1,099,511,627,776 | Binary |
| Megabit | Mb | 125,000 | Decimal bits |
| Gigabit | Gb | 125,000,000 | Decimal bits |
The binary units with an i (KiB, MiB, GiB) were defined to end the confusion, but most software still shows binary sizes with the decimal names.
File size and download time
Four common connection speeds. Slide the file size.
Going from 10 Mbps to 1 Gbps cuts a 1 GB download from about 13 minutes to 8 seconds. The bars show how much of the slowest time each speed needs.
How to convert file sizes
Know which system you are in. Step through it.
Find the unit
Is it MB (decimal) or MiB (binary)? Windows shows binary as MB.
When a cloud service, email or website lists a limit like 25 MB, it almost always means decimal megabytes.
Decimal or binary
Two systems, one name. Pick a system.
Used by drive makers, networks and most websites. Each step is 1,000.
Used by memory and by Windows when it shows sizes. Each step is 1,024.
Used for network speeds. One byte is eight bits.
That is why a new 1 TB drive shows about 931 GB in Windows. No space is missing; the two numbers measure the same bytes in different units.
Before sending a large file
Avoid failed uploads and bounced emails. Tick each item.
Tick each item as you go.
Email attachments are encoded, which adds about 33%. A 20 MB file becomes about 27 MB in transit and can bounce off a 25 MB limit.
What you get
Every unit in one place. Each tile explains one result.
The exact size behind every unit.
Decimal units used by drives and websites.
Binary units used by Windows and RAM.
For comparing with internet speeds.
At the speed you entered.
The calculator keeps full precision in bytes, so converting back and forth never drifts.
Frequently Asked Questions
No question matches that search.
How many MB are in a GB?
1,000 in decimal units. In binary units, 1 GiB is 1,024 MiB.
Why does my 1 TB drive show 931 GB?
The maker counts 1,000,000,000,000 bytes. Windows divides by 1,024 three times and shows 931 GiB, labelled as GB.
How long does it take to download 1 GB?
About 80 seconds at 100 Mbps, 13 minutes at 10 Mbps and 8 seconds at 1 Gbps.
What is the difference between Mb and MB?
Mb is megabits and MB is megabytes. 1 MB = 8 Mb.
Is a KB 1,000 or 1,024 bytes?
Officially 1,000. 1,024 bytes is a KiB, though many programs still call it a KB.
How big is a 4.7 GB DVD in GiB?
About 4.38 GiB.
How do I convert Mbps to MB/s?
Divide by 8. 100 Mbps is 12.5 MB/s.
Know exactly how big it is
Enter the size and unit, and the calculator shows it in every system along with the transfer time. Check whether a limit means MB or MiB, allow for overhead and you will not be caught out by a failed upload again.
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