We really appreciate all the feedback that we get through our contact form each day. A question that comes up quite often is “What is the maximum recording time of camera XY”, or, “How much recording time do I get with a 32GB card (64GB card, etc.)?”.
The answer to this question applies not only to dashboard cameras of course, but to any digital video camera. This article will show you how to calculate exactly how much video footage you are going to get with any given camera setup, and we will also give you a simple rule-of-thumb formula that allows you to all but calculate the recording time in your head.
NOTE: If you don’t care about the math and just want a quick and dirty formula to calculate the recording time of any camera, just skip the next couple of paragraphs and continue reading at “Quick Formula”.
The reason why we do not usually state the recording capacity of the cameras in the reviews is because it depends on several factors. One factor is of course the size of the memory card (SD card) used, and the other factor is the camera’s bit rate. When both of these are known, you can calculate the maximum recording capacity using a simple formula.
Bear in mind that you can reduce the bit rate by lowering video resolution. For example, if your camera’s maximum resolution is 1080p but you set it to 720p, obviously this will allow you to record more video footage than when you record in 1080p mode.
Calculating Recording Time
So based on the size of the memory card and the bit rate, how can we calculate the total recording time?
Let’s say you are using a Street Guardian SGGCX2 with a 256 GB SD card. You are running your device at a 1080p resolution for best video quality, resulting in a bit rate of approximately 15 Mbps. Mbps means “Megabit per second”, so each second of video consumes 15 million bits.
256 GB are 256 Gigabyte, or 256 billion bytes. 1 byte has 8 bits, so the capacity in bits is 256*8=2048 Gbits. Divide this by 15 Mbits and the result is the number of seconds you can record.
256,000,000,000*8⁄15,000,000 = 256,000*8⁄15 = 2,048,000⁄15 = 136,533.33
136,533.33 seconds divided by 60 are 2275.55 minutes, which equals 37.93 hours. In other words, with a 256 GB card the SGGCX2 can record continuoulsy for 1 day, 13 hours and 55 minutes before it will automatically start to overwrite the oldest footage.
So with GB being the card size in GB, Mbps the bit rate in Mbps, and s the recording time in seconds, our formula is
GB*8*1000⁄Mbps = s
or to get the result in hours directly
GB*8*1000⁄Mbps*3600 = 2.222*GB⁄Mbps
Quick Formula
If you just need a quick approximation of the total recording time in hours, of a dash cam or any other digital video camera, you can use this quick formula:
2*GB⁄Mbps
In other words, take the memory card capacity in GB, divide it by the bit rate, and multiply the result by 2.
The result will be about 10% less than the theoretical maximum recording time. Of course there will also be some formatting data on the card, and the space is not always used optimally. Thus, the simplified formula will give you a pretty good approximation of your actual recording time.
Always Use High Endurance SD Cards In Video Surveillance
If you use a regular memory card in a video surveillance camera, you may find out that it won’t last very long, in some cases only a few weeks or months. Why is this?
Security cameras — no matter whether it’s a dash cam, a security camera, a body cam, or any other type of video surveillance — continually write to the SD card, often even 24/7. Once the card is full, the oldest content is overwritten, and a new writing cycle begins.
Each time the data is overwritten, the flash memory on the card degrades a little bit. Regular memory cards are not designed for this type of heavy use. High endurance cards are specifically made for continuous recording, and will survive much longer.
Of course, the bigger the memory card is, the more data it will hold. As a result, there will be less writing cycles, so the card will last longer. For maximum SD card life, we recommend you get the largest card that your camera supports.
Most dash cams support 64GB these days. If your camera can handle it, it’s preferable to get a larger card though: Statistically speaking, 128GB will last roughly twice as long as 64GB, and 256GB will last you four times as long.
If you’re interested in the technical details, check out this article that goes a lot deeper into the specifics of SD cards and how they work.
