Im using a 4.5-15V DC motor,15800rpm and i want to vart the speed from stopped to full speed with a pot. Ive tried experimenting with different value pots and have burnt a couple out. Can anyone help me calculate the value the pot should be?

Im using a 4.5-15V DC motor,15800rpm and i want to vart the speed from stopped to full speed with a pot. Ive tried experimenting with different value pots and have burnt a couple out. Can anyone help me calculate the value the pot should be?