Just getting set to start the C25K program, but I am wondering what speed is considered a "brisk walk" vs. what speed is considered "jogging"? I regularly walk 25 minutes on the treadmill at 3.7mph at an incline varying between 2.1% and 4.6%, and have gone as high as 4.0mph. Even at 4.0mph, I'm not jogging...I'm walking, albeit quickly. For someone who is quite honestly JUST starting out, what would a typical speed be for jogging?
For your first intervals, try walking at 3.0 and jog at 4.5 or 5.0, and see how that feels. If you're used to walking, the initial jog intervals shouldn't be too bad for you. Good luck, and keep us posted!
...Lastly, keep in mind that one of the many goals of the program is to get you comfortable running a 5K. Weather permitting, try to do at least some of your runs outside. You'll notice a difference between the treadmill and the road, which is something you'll want to experience before tackling your first 5K.
It's not necessarily just speed, either. When you walk, no matter how fast, one foot is always on the ground and during part of each step, both feet are on the ground.. Your front foot lands before you pick up your back foot. When running, you never have more than one foot on the ground, and during part of each step both feet are off the ground. You pick up your back foot before your front foot lands.
As mentioned above, a good speed to try for starters would be around 4.5 mph, about a 13:20 mile pace. Adjust as needed.