Strongly seconding this. For anyone still hesitant, I further recommend the following experiments:
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Sample a few activities your team has completed. Check how long the 90 % smallest activities are on average, and compare it to the average of the biggest 10 %. Or the median compared to the maximum, or whatever. You'll probably find the difference is about an order of magnitude or less. In the grand scheme of things, every activity is the same size. You can estimate it as exp(mean(log(size)) and be within an order of magnitude almost every time.
Once your team has accepted that something is "an" activity and not a set of activities, don't bother estimating. For all practical intents, size is effectively constant at that point. What matters is flow, not size.
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For the above sample, also study how long passed between the "go" decision on the task and when it was actually released to customers. In a stable team, this number will be eerily close to the theoretical based on Little's law referenced in the parent comment.
Oh, and you shouldn't focus on man-hours. Work with calendar days. Not only does that simplify mental arithmetic for everyone, it's also the only thing that matters in the end. Your customer couldn't care less that you finished their functionality in "only" 6 man-hours if it took you six weeks to get it through your internal processes.
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Fun follow-up to the size experiment: now ask someone intimately familiar with your customers to estimate the dollar value of each activity. You might find that while all activities are practically the same size, they'll have very different dollar values. That's what you ought to be estimating.
This. I've found that, whatever the project is, the velocity of a team in terms what they define as a "task" is pretty constant, surprisingly so even. In the end, just counting the outstanding tasks proved to be a good estimator of where we'd end up at the deadline.
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Sample a few activities your team has completed. Check how long the 90 % smallest activities are on average, and compare it to the average of the biggest 10 %. Or the median compared to the maximum, or whatever. You'll probably find the difference is about an order of magnitude or less. In the grand scheme of things, every activity is the same size. You can estimate it as exp(mean(log(size)) and be within an order of magnitude almost every time.
Once your team has accepted that something is "an" activity and not a set of activities, don't bother estimating. For all practical intents, size is effectively constant at that point. What matters is flow, not size.
----
For the above sample, also study how long passed between the "go" decision on the task and when it was actually released to customers. In a stable team, this number will be eerily close to the theoretical based on Little's law referenced in the parent comment.
Oh, and you shouldn't focus on man-hours. Work with calendar days. Not only does that simplify mental arithmetic for everyone, it's also the only thing that matters in the end. Your customer couldn't care less that you finished their functionality in "only" 6 man-hours if it took you six weeks to get it through your internal processes.
----
Fun follow-up to the size experiment: now ask someone intimately familiar with your customers to estimate the dollar value of each activity. You might find that while all activities are practically the same size, they'll have very different dollar values. That's what you ought to be estimating.