Typical speed tests on a Mac or iOS device use a sequence of data block sizes to calculate a point to point speed from a distant server. The resulting number in Mbps, while useful for analysis of overall service, file downloads and browsing, doesn't reflect what you'll actually get from Netflix. Here's how to see your actual Netflix delivery data rate.
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Netflix doesn't try to saturate your internet connection delivered by your Internet Service Provider (ISP). For example, if you're paying for a 12 megabits per second (Mbps) connection, Netflix won't try to use all of it just to generate a slightly better picture.
Note: communication rates are always expressed in bits per second (bps), not bytes per second (Bps).
It turns out, from what I've seen, Netflix will dynamically increase the speed of the connection depending on the quality of your ISP service, but only up to about 3 Mbps for high definition video. (You must have HD video enabled in your account settings. See below.)
Streaming plan is in the Netflix account settings.
For example if your connection is a slow 1.5 Mbps DSL service, Netflix will start streaming at several hundred Kbps and then increase the data rate until it peaks at one of the standard plateau levels closest to but under our example 1.5 Mbps, namely 1.050 Mbps. However, if you have that 12 Mbps ISP service, the rate will start climbing until it reaches the cap of 3.0 Mbps and generally remain there for your session.
Apparently, 3.0 Mbps is the lowest rate that supports a decent looking 720p HD picture, and I surmise Netflix can deliver the best possible picture to lots of customers without gobbling up (and paying for) massive bandwidth.
Calculating Your Netflix Speed
1. You must be logged on to your Netflix account.
2. Using the Netflix search bar, look for the video "Example Short 23.976." This is a special video, with lots of different sample scenes, which displays the data rate, resolution and quality in a text overlay.
3. Play the video and look for the data rate and resolution superimposed on the video as it rises towards the HD peak of 3.0 Mbps and 1280 x 720p. The data rate and resolution may fall short if your ISP service is lower than than 3.0 Mbps or if you only have standard definition service.
Here's a sample of what I got, at first, and then when the stream stabilized on my iMac. Note: Pixel Aspect Ratio (PAR) = 4:3 for standard definition and 1:1 for high definition.
Bitrate started at 560 Kbps, standard definition
In a few seconds the picture visibly improved and stabliized. (The improvement isn't quite so evident in these two screen shots.)
Bitrate peaked at 3.0 Mbps, high definition
By way of comparison, here's what I got on the iMac with Firefox and speedof.me at the same time. That's a great speed test, by the way, because it doesn't depend on Java or Adobe Flash. The story here is that while you may have special needs for lots of bandwidth for other purposes, that won't improve your Netflix throughput. That is, until 4K streaming is routine — which requires about 40 Mbps. It appears to me that providers like Netflix may try to get by with considerably less.
Analysis
If you have an excellent ISP data rate, and you're not geting the 3.0 Mbps that Netflix usually provides in HD mode, there may be a problem with your ISP service. For example, there may be a dustup going on between Netflix and your ISP. Or it could be a temporary disruption in the quality of service, so try again later. On the other hand, I have read about a few special cases where customers got well over 4 Mbps, but it's a special tier from Netflix called SuperHD and may not be available to all customers.
Finally, Netflix publishes a list of how ISPs are doing in the U.S. and other countries. You can view the full results for your own ISP and see how it compares to the others on average.
Netflix rates the ISPs
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House of Cards image via Netflix