This calculator estimates the minimum number of trials you will need to fit a specific model. It also estimates the total amount of work you can expect by adding 3 extra trials and 8 replicates to this minimum number.
It's best to add at least 3 extra trials in a real experiment.
You will also want to add at least 8 runs more than the minimum to judge the quality of your data.
(Note: If you're really budget limited you can often get away with 5 runs more than the minimum as long as you are careful to test your Sweet Spot before reporting it.)