The calculator below helps you estimate how long it will take to download a file using TCP. TCP is
the unsung hero that makes sure websites load properly and files arrive safely on your computer.
As you adjust the numbers in the calculator, you'll see the estimated download time update
instantly below.
Settings
File size:
Ping latency between client and server:
Bandwidth of connection between the client and server:
Client type:
Internet Protocol Version:
Results
Approximate Download Time:
Round Trips to the Server:
What is TCP?
TCP, or Transmission Control Protocol, is a set of rules that lets computers reliably exchange
information over the internet. Without it, sending a file across the internet would be a disaster!
Here's why TCP is so important:
No Lost Pieces: Imagine sending a puzzle, and some puzzle pieces go missing. Without TCP, the
receiving computer wouldn't even know that parts of the puzzle never arrived. TCP makes sure all
the pieces of a file arrive at the destination.
No Corrupted Data: What if some puzzle pieces got warped or damaged? TCP ensures the data
received is exactly the same as the data that was sent.
Right Speed, Every Time: If a sender sends a file too quickly, parts of the file can get lost.
If the sender sends the file too slowly, then the receiver is left waiting forever. TCP manages
the speed, ensuring a smooth and efficient data transfer.
TCP solves all of the problems above, which is why it's the standard for moving data across the
internet.[] In fact, your device used TCP to load this webpage!
Why is Estimating Download Time with TCP Tricky?
TCP doesn't download files at a steady pace. It's like a car starting from a stop: it begins
slowly and gradually speeds up until it reaches the maximum speed your internet connection allows
(your bandwidth).[,,]
For Large Files: When you're downloading a big file, your internet's bandwidth is usually the
main factor determining how long the download takes. Once TCP gets up to speed, the download
rate follows your connection's capacity. So, for large files, knowing the file size and your
bandwidth gives us a good estimate of the download time.
For Small Files: Small files are different. They often finish downloading before TCP reaches
full speed. In these cases, your ping latency becomes the most important factor. Ping latency is
the time it takes for a tiny piece of information to travel from the sender to the receiver and
back.
If the ping latency is low, TCP can speed up quickly.
If the ping latency is high, TCP has to increase its speed more slowly.
Because the main factor affecting download speed changes based on the file size, the ping latency,
and the bandwidth, estimating TCP download times can be complex. This calculator handles this
challenge by dynamically switching between different mathematical models to give you the most
accurate estimate for a specific situation.
Limitations
This calculator does not account for packet loss, meaning that in any real-world system, the
actual download time would probably be greater than the estimate given above.
Additionally, this calculator assumes the sender already knows the bandwidth. In the real world,
systems determine the bandwidth by observing how many data packets get lost in transit.