Call the customer support for the brand(s) of phone & tablet you have. There usually is a limit, but it varies according to make and model. The customer support can tell you the limit of the model(s) you have. Also they can recommend what SD cards will perform the best and be the most reliable for your devices (be sure to ask for those recommendations, not just the size limit), . With the information from the customer support for your device you will know the exact size, brand, and version of SD drive to buy. Then look around to see who sells those exact ones on places like Amazon, e-bay, Best-buy, and any others.