You're on /r/bodybuilding not /r/Fitness

But a pump is an increase of blood flow into a muscle by engaging it over a period of time causing it to engorge and appear bigger and more full. The size of your pump depends on a lot of factors.

For instance, if I train my arms - both my triceps and my biceps - and then measure my arm, my pump usually adds around an inch to my arms, maybe a little more.

You'll know when you have a pump, especially in your arm, because your arm will be engorged and hard to bend. Take some dumbbells and curl. Slow and controlled rep. Flex the muscle during the contraction and release slowly back to the starting position.

Keep doing that and different variations and you'll eventually get a pump.

If you get some sodium and carbs in before your workout, you'll likely get a better pump. A pump is also dependent on what is in your body during the time of exercise and is affected that way as well.

My pumps usually last anywhere between 30 minutes to maybe an hour / hour and a half, depending? Then it goes and deflates back to normal.