Our example card holds 16 Gigabytes of information. Nice for evaluating cards but I what does that really mean. For how much stuff a card will hold page down. The next section describes what a giga and tera byte are.
First we need to start off at the basic level of a bit. A bit is the smallest memory unit and is read by the machine as a 0 or 1 or on and off. If all you have to describe to things is zero and one its hard to say anything. So the PC places 8 bits together; that gives you many more options to describe things and is called a byte. In short the computer alphabet only includes zero and one and all words are eight letters long.
A byte is a basic unit like meter or litre, to keep count a prefix is added. So one thousand meters is a kilometer. If "A picture says a thousand words" you could just say "A picture says a kiloword". We will get to how big a picture is soon. But first lets define the prefizes we will see on SD cards.
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MB or Mega as in Megabyte is 1,000 Kilobytes or 1,000,000 bytes
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GB or Giga as in Gigabyte is 1000 Megabytes or 1,000,000,000 bytes
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TB or Tera as in Terabyte is 1000 Gigabytes or 1,000,000,000,000 bytes
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The price will remind you, but if you know Mega is smaller than Giga and Tera is huge you have the picture. Im using the smallest definition here for various technical reasons a Megabyte might be 1,048,576 bytes; if your card reads higher consider it a bonus.
The controller will save and use some of the space to record things like the volume label and format, so your card may not show the full amount as available. The controller will also block bad sectors. If you are showing less than 75% of the rated size I would return that card.
For the part you are interested in how much stuff will a card hold. First there are many formats and sizes of pictures and music. I will outline some common ones here these are very conservative estimates - If you get more consider it a bonus.
Also remember the manufacturer of the device will have much more accurate figures for your photo and video devices.
Photos
I will use jpeg as the standard or file type we store the photos in. Most cameras can shoot in High or Low quality modes and many in-between. Digital Cameras are rated in pixels this is a rough estimate
To store one pixel you need half a byte.
So 1 Gigabyte will hold roughly 1500 low resolution photos or 54 high resolution ones.
There are other variables but here is a conservative estimate based on pixels.
The following is the number of full resolution pictures per giga byte.
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6 Mega pixel camera - 450 pics per gigabyte of memory minimum
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8 Megapixel camera - 300 pics per GB of memory minimum
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10 Megapixel camera- 200 pics per GB of memory minimum
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12 Megapixel Camera - 150 pics per GB memory minimum
Music
For music we will use the MP3 format the tricky part here is the sampling rate. 256 kilobits per second is CD quality. The sampling rate will be an option on the software you are using to copy to the card. The lower the number the lower the quality and the more songs you will get on your card.
The following is based on a 4 minute song and 60 minute CD.
1 Gigabyte will hold
Sampling Rate Minutes Songs CD's
256 kbps 550 135 9
196 kbps 700 175 11
Video
Video is a combination of music and sound so even more variables are involved. Video is rated in Megabit per second or Mbps. Here is a conservative estimate of what to expect.
6 Mbps - Extended Quality - 20 minutes per GB of memory
9 Mbps - Standard Quality - 15 minutes per GB of memory
13 Mbps - High Quality - 10 minutes per GB of memory
One thing to remember when you make a file the device will write a file header with the filename ect. So 20 1 minute videos will take more space than one 20 minute video.
