ADSL speed is determined by the type of ADSL broadband you can access (as there are two basic types) and the distance between you and your telephone exchange. You can measure your broadband speed using our ADSL speed test below. The maximum ADSL speed (i.e. downlink connection speed) for basic ADSL is 8 Mbps. If you have the more modern variant of ADSL called ADSL2+ on your line, the maximum downlink connection speed is 24 Mbps. Sadly, only very few broadband users who are located close to the exchange can achieve anywhere near these speeds. This is because broadband signals usually have to travel considerable distances along the copper cable from the exchange to the street cabinet, and then along another cable from the street cabinet to you.
Your ADSL speed depends on the type of ADSL and the distance from your exchange
The broadband signal from the exchange suffers attenuation (loss) as it travels along the cable from the exchange to your broadband modem, reducing the speeds that can be delivered. In general, the longer the total distance between your modem and the exchange, the more that signals are attenuated, as shown in the chart below.
Chart of ADSL2+ and ADSL connection speed against distance from the exchange
ADSL speed depends critically on the type of ADSL you have on your line. Basic ADSL is the oldest, ‘first generation’ ADSL broadband, and delivers downlink connection speeds up to 8Mbps. 99.8% of UK homes and businesses have access to this. ‘Second generation’ ADSL2+ technology is able to achieve higher speeds (up to 24 Mbps) by using double the bandwidth of ADSL. ADSL2+ is now available to 98% of UK homes and premises.
As seen in the chart above, ADSL2+ provides most benefit for premises close to the exchange, and speeds in excess of 15 Mbps can be achieved within about 2 km of the exchange. For distances between 3 km and 3.5 km, where ADSL speeds have fallen well below 10Mbps, ADSL2+ still provide worthwhile increases in connection speeds. There is very little difference in performance between ADSL and ADSL2+ at distances above 4 km.
Note that the length of the cables between your location and the BT exchange may be considerably more than the direct distance between your location and the exchange ‘as the crow flies’. This is because the cable first travels to a street cabinet, and there may be a number of possible routes.
Measure your connection with our accurate ADSL speed test
Online speed tests are typically the easiest way to estimate the speed of your ADSL broadband connection, but beware inaccurate results. Below is our online speed test, provided by Ookla.
To get an accurate measurement of your ADSL speed:
- ensure there are no other programs or applications running in the background
- ensure there are no other devices using your ADSL connection
- try different servers to avoid overloaded or distant servers
- run your speed test on a device connected to your router by Ethernet cable if possible.
Also, note that the speed test measures throughput, which is different to (and lower than) connection speed. If you have a connection speed of 20 Mbps with ADSL2+, for example, your maximum throughput will be 19 Mbps. With a 10 Mbps connection speed, maximum throughput will be 9 Mbps.
If you are disappointed with your ADSL speed and/or feel that measured speeds are lower than you would expect from our speed versus distance chart, then you may be able to significantly increase speeds by reading our Increase Broadband Speed Guide. Methods to boost ADSL speed, covered in our guide, include:
- fitting a filtered faceplate
- locating your modem next to the master socket
- tweaking the target SNR margin using a compatible modem
- migrating to ADSL2+ if you are currently using ADSL, if you can.
- connecting devices (where possible) using Ethernet cables rather than WiFi
- optimising WiFi connections (e.g. using 5 GHz instead of 2.4 GHz, employing additional WiFi Access Points to boost coverage and choosing WiFi channels with care to minimise interference).
In conclusion, it is important to be realistic about your ADSL speed. Only those very close to the exchange will be able to achieve over 20 Mbps with ADSL2+ and most people will achieve ADSL speeds much lower than this. If you are a long way from the exchange (e.g. more than 4 kilometres), then you can expect just a few Mbps. Particularly in this case, our speed enhancement tips could make a significant difference.
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