Today’s Question: How much extra disk space in my catalog do smart previews consume?
Tim’s Quick Answer: Smart Previews in Lightroom consume a surprisingly small amount of storage space. As a general rule you can expect Smart Previews to consume somewhere around 1MB per image, with your specific results depending on the nature of the images being processed.
More Detail: A Smart Preview is essentially an Adobe DNG file resized to no more than 2,540 pixels on the long side. Because there is lossless compression applied, the file sizes are quite small. In my testing I have found that the Smart Preview file size represents approximately 1MB per image. This total can vary considerably based on the types of image files you’re working with, and the effectiveness of compression based on the contents of the photos.
But I think the 1MB per image value represents a good general estimate. That, in turn, translates into about 1GB of storage space for every 1,000 images. For a catalog with 100,000 images, you could expect the data file for your Smart Previews to be about 100GB.
Again, these are just rough estimates, and the actual result can vary significantly based on the types of source images you’re using along with other factors. But the point is that compared to the storage requirements for the original captures, Smart Previews are quite small and manageable.