One of the first questions you’ll ask when in the planning stages of a new Wi-Fi project will be how many access points are needed. There are various factors which will affect the answer to this:
– Coverage area – floor plan
– Shape of area – floor plan
– Building – wall material
– Number of users
– Capacity/Throughput requirements per user/application

The more information you have, the more accurate you can be with your estimate of how many access points you’ll need for reliable coverage. If you follow our blog, you’ll have read our previous posts about site surveys. These are a great way of getting detailed data about coverage, building materials and potential causes of interference, so not only will you get the best advisories for number of access points, but also the best places to put them and other bits of wireless kit.

Without knowing the details above, the estimate would be extremely rough, and you would be taking a bit of a risk on any purchases made.

You might be able to get a rough estimate for a certain number of access points per number of users, or by square footage, but these don’t take into account any of the other variables that could significantly affect coverage.

Let’s take a look at each factor in a bit more detail.

Coverage Area

The best place to start is finding out how big the space is in square feet (or metres). Some rough estimates might give you a basic guide of 1 access point to every 1600 square feet, but these are based on some very simple assumptions on that given space.

For this ratio of access point to space size to work effectively, the office would be:
– A typical office or residential space
– Square or rectangle in shape (no nooks or crannies)
– A single floor area (not multiple levels)
– Built with drywall partitions or cubicles (not thick concrete or brick behind dry wall facades)
– Basic internet and streaming requirements

Basically, the simplest of the simple.

Shape of Area

This goes one step further than just making an estimate based on size alone. Knowing the shape of the area gives a much clearer picture of whether one access point will be sufficient for the size. A rectangle shape with a size of 1600 square feet will have a very different access point requirement to a space of the same square footage but in the shape of an L, T or an H.

It wouldn’t be possible to place an access point that would be in a central location for all users, without the signal being affected by multiple exterior or interior walls.

A general rule of thumb in these situations is:
– For an L Shape space, multiply the square footage estimate by 2
– For a T Shape, multiply the square foot estimate by 3
– For an H Shape, multiply the square footage estimate by 4

Building Material

So you’ve worked out the square footage, and you know the shape of the room – Next on your list for making a more accurate estimate is knowing the building material in each wall.

If any of the walls are built with brick, cement or cinderblock, then the number of access points you will need will increase.

A very basic guide to how many access points you would need in a building made of these types of materials would be one to every 800 square feet, but we wouldn’t recommend you make purchases based on this basic idea.
Remember, it’s not just about the access point signal reaching your users, but the lower power user signa; getting back to the access point.

Number of Wireless Users/Devices

The estimate for the number of access points you need is improved further by knowing how many people will be using your Wi-Fi. This is particularly useful for places like lecture halls, auditoriums, stadiums and other places for a large number of users.

As an example, let’s look at two ways to work out an estimate for a sports stadium.

If you based it on the standard size estimate, based on a stadium that seats 80,000 peoplewith dimensions of 650 x 750 feet, you would need to do 487,500 divided by 1600 (square feet per access point from above) which would give you an estimate of 305 access points to cover this area.

However, you could also estimate it based on user count. Let’s say that only 50% of the attendees connect to the Wi-Fi, and out of those users only 25% actively use Wi-Fi at any given time. If you base it on 30 users per access point, then you would need 334 for an 80,000 seat stadium. This would be a better estimate in terms of coverage.

Applications/Wi-Fi Usage/Capacity

Taking into consideration all of the above influences on your estimations is great, but they don’t also factor in what can make Wi-Fi inefficient in denser user environments.

An alternative estimation would be basing it on capacity requirements. If we stick to the stadium example, then we’d work it out as follows…

Select a per user throughput number: 1 Mbps / 1000 kbps
Estimate percent of users that will connect to WiFi: 50% adoption rate / take rate
Estimate percent of users active on network as same time: 25%
Target throughput per AP/RF efficiency: 20 Mbps per AP (5 GHz)

1. AP Throughput Divided By User Throughput = Users Per AP
20 Mbps / 1 Mbps = 20 users per AP sharing 20 Mbps

2. Users Per AP Divided By Active Users = Serviceable Users Per AP
20 / 0.25 = 80 user seating area (only 1/4 will be active on WiFi at same time)

3. Serviceable Users Per AP Divided By Take Rate/Adoption Rate = Service Area/Cell Size
0 / 0.5 = 160 user per cell/seating area (1/2 will connect to WiFi)

4. Stadium Spectator Capacity Divided By Service Area = AP Count
80,000 seat stadium / 160 users per cell/seating area = 500 APs

When initiating the design phase, the more detailed your approach the more reliable your Wi-Fi will be. Taking into consideration all of the above factors will help build a clear picture of your environment and make your estimations on access points as accurate as possible.