Waffle supports sizing cards using story points. We chose Fibonacci-like numbers 1-100 based off of the commonly-used "Planning Poker" method. This is a great way for your team to size cards.
Story points do not equal hours -- they are used as a comparison of complexity/effort/doubt between cards. If a card has 3 points, it should be three times as difficult as a 1 point card.
If you run into a card that is sized 13 points or higher, it generally means one of two things:
A) The card is not well enough defined
B) The card should be broken down further into multiple cards
If your teams chooses to make all cards the same size, then you can just count the cards completed at the end (aka throughput) and don’t need to add specific sizes to each card. Story point sizing comes in most handy if your team is like ours, where some cards take 4-5 days and others may only take 1/2 day.
As long as you are consistent in your estimates, you will soon see a pattern and know how many story points your team can do in a week/2 weeks/iteration (aka velocity) helping you better plan in the future.
Story points are not designed to measure your team's task hours or track your team's capacity (how many hours are completed in a set time frame).
Below is a segment from CA Technologies' guide to sizing and estimating user stories (if you're having trouble or want to learn more, we highly suggest checking this out).
User stories in your product backlog should be estimated in terms of their relative size. Once you have numbered your product backlog like this, you can measure how many of these units you are getting done each iteration by adding up the numbers for each accepted story. Over time, if you keep your team together, this velocity number should stabilize. If your velocity has been about 15 in the past, you can predict that if the team stays the same, you will get 15 done each iteration moving forward.