Transfer time

How Long Does It Take to Upload 20 GB at 100 Mbps?

Uploading or downloading a 20 GB file at 100 Mbps takes about 26 minutes 40 seconds, assuming the full speed is sustained.

By the HeftySend team Last updated 8 October 2026 Free, no sign-up

Upload or download time

26 min 40 s

100 Mbps is 12.5 MB/s. 20 GB is 20,000 MB, and 20,000 ÷ 12.5 = 1,600 seconds.

With 10% protocol overhead: about 29 minutes 20 seconds. Assumes the speed holds for the whole transfer.

Calculate your own

Different file size, a speed in MB/s or Gbps, or the 10% overhead switched on? The calculator opens pre-filled with 20 GB and 100 Mbps; change either value and the answer and both reference tables update.

Open the calculator: 20 GB at 100 Mbps

Works without JavaScript; the result is in the page when it loads.

What 20 GB actually is

Twenty gigabytes is a 500-frame RAW photo shoot at about 40 MB a frame, a full afternoon of 4K from a phone or mirrorless camera, a modern indie game, or a quarter's worth of client deliverables zipped together. It is the size of a typical wedding or event photography hand-over.

A 20 GB transfer is long enough that something will interrupt it on a slow link: a laptop lid closing, a Wi-Fi roam, a mobile hand-off between cells. Splitting it into several transfers does not make it faster, but a resumable upload makes an interruption cost seconds instead of a restart from zero.

4K video (55 Mbps): about 48 minutes
1080p video (15 Mbps): about 3 hours
RAW photos (40 MB each): about 500
25 MB email attachments: about 800

What 100 Mbps actually is

100 Mbps is the most common advertised home broadband speed and the number most people put into a calculator. Downloading at 100 Mbps is everyday; uploading at 100 Mbps means full fibre (FTTP), a symmetric business line or a lucky 5G cell. It moves 12.5 MB of file data a second.

Is 100 Mbps a realistic upload speed? Cable plans sold as 100 Mbps typically upload at 10–20 Mbps, so if you are sending rather than receiving on cable, the 10 Mbps and 25 Mbps figures are usually closer to what you will see. On fibre, 100 Mbps up is a modest, reliably sustained speed.

20 GB at other speeds, and other sizes at 100 Mbps

The first table keeps the file at 20 GB and changes the speed; the second keeps the speed at 100 Mbps and changes the file. Rows with their own write-up are linked. Every row is also written out as a sentence under "In words".

20 GB at neighbouring connection speeds
Connection speed	Time for 20 GB
25 Mbps	1 h 46 min
50 Mbps	53 min 20 s
100 Mbps	26 min 40 s
500 Mbps	5 min 20 s
1 Gbps	2 min 40 s

In words

20 GB at 25 Mbps takes about 1 hour 46 minutes.
20 GB at 50 Mbps takes about 53 minutes 20 seconds.
20 GB at 100 Mbps takes about 26 minutes 40 seconds.
20 GB at 500 Mbps takes about 5 minutes 20 seconds.
20 GB at 1 Gbps takes about 2 minutes 40 seconds.

Neighbouring file sizes at 100 Mbps
File size	Time at 100 Mbps
5 GB	6 min 40 s
10 GB	13 min 20 s
20 GB	26 min 40 s
50 GB	1 h 6 min
100 GB	2 h 13 min

In words

5 GB at 100 Mbps takes about 6 minutes 40 seconds.
10 GB at 100 Mbps takes about 13 minutes 20 seconds.
20 GB at 100 Mbps takes about 26 minutes 40 seconds.
50 GB at 100 Mbps takes about 1 hour 6 minutes.
100 GB at 100 Mbps takes about 2 hours 13 minutes.

Why it usually takes longer than 26 minutes 40 seconds

Protocol overhead

The headline figure assumes every bit of the 100 Mbps carries file data. In practice TCP/IP headers, TLS and HTTP framing take 5–10% of the link, so a more realistic estimate for 20 GB at 100 Mbps is about 29 minutes 20 seconds with 10% overhead, 2 minutes 40 seconds longer. Quote that figure when someone is waiting for the file.

Upload is not download

The formula gives the same 26 minutes 40 seconds for an upload and a download, but the speed you should plug in is rarely the same. 100 Mbps is usually the download speed of a plan; on an asymmetric cable, 4G or satellite link the upload side of that plan is often around 10 Mbps, which turns 26 minutes 40 seconds into about 4 hours 26 minutes for the same 20 GB. When you are the one sending, run a speed test and use the upload number.

Dropped connections

Over 26 minutes 40 seconds something can interrupt the transfer: a Wi-Fi roam, a laptop lid, a mobile hand-off between masts. A plain browser upload starts again from zero; a transfer that uploads in parts and resumes from the last confirmed part loses seconds. HeftySend uploads are resumable by default; the single button below takes you to the uploader.

Sending something big? Let it survive a dropped connection.

HeftySend uploads in parts and resumes from the last confirmed part, so a Wi-Fi blip or a sleeping laptop costs seconds, not the whole transfer. No account needed for transfers up to 100 GB.

Send up to 100 GB free

Frequently asked questions

How long does it take to download 20 GB at 100 Mbps?

About 26 minutes 40 seconds, the same as uploading, because the formula is file size divided by speed in both directions. The practical difference is that 100 Mbps is far more likely to be a real download speed than a real upload speed: plans advertise the download figure, and on cable, 4G and satellite the upload side is a fraction of it. If you are downloading 20 GB on a 100 Mbps plan, this estimate is usually close; if you are uploading, measure your upload speed first.

How long does 20 GB take at 100 Mbps with protocol overhead?

About 29 minutes 20 seconds once you allow 10% for TCP/IP headers, TLS and HTTP framing, which is 2 minutes 40 seconds longer than the raw 26 minutes 40 seconds. Real transfers lose 5–10% of the link rate to that framing, so the overhead figure is the better one to quote when someone asks when 20 GB will arrive.

What if my connection only manages half of 100 Mbps while sending 20 GB?

Transfer time scales directly with speed: at 50 Mbps the same 20 GB takes about 53 minutes 20 seconds, and at 25 Mbps about 1 hour 46 minutes. Wi-Fi, other devices on the network, a busy receiving server or a laptop on battery can each take a connection well below its headline figure, so a speed test taken right before you send is the only reliable input.

How many megabytes per second is 100 Mbps, and how does that give 26 minutes 40 seconds for 20 GB?

100 Mbps is 12.5 MB/s, because there are 8 bits in a byte. 20 GB is 20,000 MB, and 20,000 ÷ 12.5 = 1,600 seconds, which is 26 minutes 40 seconds. The calculator uses decimal units (1 GB = 1,000 MB); a file that Windows reports as 20 GB is about 7% larger in decimal terms and takes correspondingly longer.