Well, if you just want a picture of it, here you go. I backed off until I was just out of the range where the red warning icon for the grenade appears, and took no damage when this grenade exploded.
Honestly, though, I'm not sure how this screenshot is going to help you any more than playing a bit will. You'll quickly get a feel for it. The simple rule is if you can see the warning icon flashing, keep running.
Two things of note:
- If you can see the red warning icon flashing for the grenade, you will take damage when it explodes unless you're behind cover.
- If you are directly on top of the grenade, a single roll is not enough to take you out of its radius, but two rolls is.