We spend way too much time hassling around with estimating our work. That time would be far better spent improving the sizing of work rather than how long it will take us to do the work. (I'd encourage you to go read up on flow through systems, as good sizing of work items is crucial!)
Also, I'm not going to get pulled into the #NoEstimates debate. There's a time and need for everything.
Some teams get carried away with long sets of Fibonacci numbers, extravagant planning poker, etc.
I'd say throw all that out and focus on simple t-shirt sizing: Small, medium, and large. That's it.
Small should be things you're confident you can get done in a day or less: Think about building and testing a login screen when you've got existing authentication infrastructure in place.
Medium and large are simply variants of that. "Oh, this seems a bit bigger than a login screen, but not significantly so. We'll call it a medium."
Note there's no Extra Large, Double-X, or Ginormous on my list. I'm adamant that really large efforts need to get pushed back into planning and split into smaller chunks.
Really large work is high risk. Minimize the amount of high-risk work you take on.
Stop overthinking your estimating. Spend more time breaking things down into small chunks of work.
NOTE: Testers, the above applies to you when you're asked to give an estimate of how long it's going to take to test. Start with your smallest task and go from there. Push back HARD on things that are too complex, too big, too risky. Ask to break those tasks down!
