What Does 3Mbps Mean for an Internet Service Plan?

By John Lister

Updated August 29, 2017

Speed is only one factor to consider when choosing a broadband service.
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A cheap broadband deal that doesn't offer a fast enough connection for your needs is a false economy leading to frustration. When you see terms such as 3 Mbps in advertising for broadband services, it almost always refers to the maximum download speed that you can expect to receive. Check the terms and conditions carefully before signing up, though: this speed may not be guaranteed and you may face other limitations on data use, like a monthly data transfer cap with additional charges for overuse.

Download vs Upload

Internet service providers quoting a speed figure almost always refer to the download speed. The upload speed on the same service will usually be considerably slower. This disparity achieves the most efficient balance of cost and reliability because the average Internet user is likely to download much more data than he uploads. This doesn't apply to everyone though: people who use file sharing services or upload large files such as online video may need high upload speeds. The big difference between the download and upload speeds is why the term "asynchronous" is used in "asynchronous digital subscriber line," or ADSL, the name given to a popular technology for providing broadband over an ordinary telephone line – the speeds are not synchronized.

Data Equivalents

The term 3 Mbps means the connection transfers three megabits (3,000 bits) of data every second. A megabit is not the same as a megabyte. 3 Mbps equals 0.375 megabytes or 375 kilobytes every second. As a rough example guide, this speed should let you download a three-minute MP3 song file in around 11 to 12 seconds. A 4.7GB DVD movie file would take about three and a half hours to download.


The speeds advertised by Internet service providers are estimates and represent the theoretical maximum possible speed. According to the FCC's 2013 Measuring Broadband report, ISPs actually achieved between 80 percent and 140 percent of their advertised speeds on average. In every case, speeds were slightly lower at peak times (weekday evenings) than across the week as a whole.


Download speeds do not tell the whole story. While download speed measures the total time files take to download, another factor, latency, measures how quickly your computer can send and receive a packet (the smallest chunk of data online.) Latency varies significantly across providers and across broadband technologies. A high latency, meaning a slow response, can affect performance in both online gaming and Skype-style voice over Internet protocol services, even if your download and upload speeds are both impressive.


Some Internet providers place limits on how much data you can download and/or upload. This could be during a particular period (such as an evening) or across an entire month. Exceeding this limit could mean your service is slowed down or you face other consequences. Usage limits are particularly common on mobile broadband services. The result is that although your service may offer a particular speed such as 3 Mbps, you may not be able to download at this speed indefinitely.