Short answer: You choose.
Long answer: All Mint Mobile plans allow you to choose how much 4G LTE data you need each month—3GB, 8GB or 12GB. When you hit this limit, we don’t cut you off, we just slow it down. If you need more data, then you can do a one-time data purchase of either 1GB or 3GB. Or if you find you are hitting the limit each month, simply upgrade your plan to the next data level at any time.
Need help figuring out how much juice you can get out of your monthly data check out our blog.