How do you measure progress in BJJ (or any martial art for that matter)? It can be quite a nebulous task to say the least. Obviously there are belt rankings, but there can be (and often it's required by international committees) years between belt promotions. Some, though certainly not all, gyms add stripes (up to four) to belt ranks, but even then you'd be looking at 4 - 6 month intervals.
The "Am I Getting Less Bag" Strategy
This is simple and effective at every rank. When you begin as a white belt, you get your butt kicked, bad, and regularly. However, you might notice that you tap (are submitted) only four times in a round instead of five against your favorite training partner. Eventually you will start to "survive" longer and longer, then progress to avoiding bad positions, then volleying for positional advantages, and finally to submitting or increasing the number of submissions completed against that opponent.
This is valid through every belt rank and as you complete the progression at your given rank (white belt vs. white belt for example), you can start the process over with the next rank up even if you're not promoted there yet (e.g. white belt vs. blue belt). And so on and so forth...
The "Number Crunching / ELO" Method
If you're looking to compete, and you should at least once, then it's a good idea to mentally keep track of the score versus your opponents during each training round so that you develop that awareness (varying of course for whatever rule set you're competing under). But, what if you're rolling with someone outside of your belt rank or weight class? It's pretty rare that ever training round every day would feature someone your belt rank and +/- one weight class.
Enter the ELO. This is a ranking system used with chess and tennis players. You can see some examples of ELO being used in BJJ floating around the interwebs (another resource). However, if you're the spreadsheet guru type, you can create your own algorithm accounting for wins / losses by points / submission as well as your opponent's difficulty (for simplicity assigning fixed values for the opponent's belt rank rather than their computed rank value).
BONUS: If you're on Instagram, share the video above and tag, and I'll send you an ELO template on Google Sheets.
The "Because People Tell You" Method
This may sound trite, but valuable feedback from higher ranking teammates is a prized possession. I'm not talking about the run-of-the-mill "good job", "your game's looking sharp today" kinds of things, but when someone (it is clear when they do) go out of their way to reference a specific improvement you've made. This is doubly true if they reference your former state; "I used to be able to submit you 3 times in a round, now I'm lucky if I can pass your guard" or "your transitions from x-guard to De La Riva guard are a lot smoother than the spazzy brutish sweeps you were trying last month."
I've used all of these methods in the past and will again in the future. If nothing else, solicit feedback from your coach. Remember, you're paying them to work for you! Ask them what you need to work on and what they think you're doing well. If they can't give you an honest assessment, find another coach.
At the end of the day you need to find a validation method that is worthwhile to you. Sometimes that will come internally and sometimes externally. We're all different in those needs. If I missed something, let me know in the comments!