Your Upload Speed Decides How Long a Transfer Takes

“I have 300 Mbps internet, so why is this taking forever?”

We get some version of this question a lot. The answer is nearly always the same: the 300 is your download speed. When you send a file, what matters is your upload speed, and on many home connections it’s a fraction of the headline number.

Download vs upload

Internet plans are sold on download speed, because most people mostly download: streaming, browsing, updates. So a lot of connections, especially cable and older DSL, are asymmetric. A plan might be 300 Mbps down but only 20 or 30 Mbps up.

Fibre connections are often symmetric (the same speed both ways), and 5G home internet varies wildly. If you’re not sure what you have, run a speed test and look at the upload figure, not the big number at the top.

When you send a file to someone, the file can only leave your house as fast as your upload allows. It doesn’t matter if the receiver has gigabit fibre. The slowest link in the chain sets the pace, and that’s usually the sender’s upload.

Megabits vs megabytes

The other trap is units. Internet speeds are in megabits per second (Mbps). File sizes are in megabytes (MB) or gigabytes (GB). There are 8 bits in a byte, so:

Your speed in MB/s ≈ your speed in Mbps ÷ 8

A 40 Mbps upload moves about 5 MB per second. Not 40.

How long will my transfer take?

Here are rough times, assuming the connection runs near its full upload speed (real-world is usually 70 to 90% of that):

File size	10 Mbps up	40 Mbps up	100 Mbps up	500 Mbps up
1 GB	14 min	3.5 min	1.5 min	17 sec
10 GB	2.3 hours	35 min	14 min	3 min
50 GB	11 hours	3 hours	70 min	14 min
100 GB	23 hours	6 hours	2.3 hours	28 min

The formula, if you want to work it out yourself:

minutes ≈ (file size in GB × 8,000) ÷ upload Mbps ÷ 60

So 25 GB on a 20 Mbps upload: 25 × 8,000 = 200,000, ÷ 20 = 10,000 seconds, ÷ 60 ≈ 167 minutes. Call it three hours.

Why this also matters for upload-first services

With a traditional transfer service, you upload the whole file to their servers, then the receiver downloads it. Your upload speed still sets the first half of that. A 50 GB upload on a 20 Mbps line takes most of a working day before the recipient can even start downloading.

With a direct transfer like BoltShare, the receiver downloads while you send. There’s no separate upload step, so the total time is roughly your upload time and no more. It doesn’t make your connection faster, but it does stop you paying for it twice.

Ways to actually go faster

You can’t change your plan mid-transfer, but you can stop wasting what you have:

• Plug in a cable. Wi-Fi, especially through walls, often can’t even reach your plan’s upload speed. Ethernet usually can.
• Pause other uploads. Cloud photo backup, OneDrive or Dropbox syncing, and video calls all compete for the same upload capacity. Pausing iCloud or Google Photos backup during a big send can make a noticeable difference.
• Send from the faster side. If your friend has fibre and you have cable, and the files exist on both computers (it happens with shared projects), let them send.
• Same building? Use the local network. If both devices are on the same Wi-Fi, a direct peer-to-peer transfer may not need to go out to the internet at all, so it can run much faster than your internet plan.

There’s more on this in our checklist for slow transfers.