These are the specs from the official Maglite website.
Length: 4.8" (121.92 mm)
Barrel Diameter: 1" (25.4 mm)
Head Diameter: 1" (25.4 mm)
Weight with batteries: 3.68 oz. (104 g)
Just a tip, though... spring for the XL200, not the 100. I got the 100 and was pretty disappointed with the features. The XL200 is just a few bucks more, it's the same size, and it's MUCH easier to use the different features.
I have an xl50, and it's a great little flashlight. Plenty bright, and I can appreciate the 2 output modes to conserve battery life. Spill and throw are also adequate for just about any situation. My only complaint, however durable the light is, it's not very ergonomic. It's round cylindrical shape lends itself to be easily dropped if your hands are greasy or wearing gloves. Therefore, it has ended up being more of a power outage light or for the car as opposed to backpacking light or emergency light for me. No holes for a lanyard and doesn't stand on end well. Still, despite these, the flashlight lives up to the maglite name and is a great flashlight to keep in the bedstand and is plenty durable.
Jamie, I've seen that 'Nu-flare' light under a different brand, and it is brighter, but you may be disappointed with quality. For the price, the Maglite XL100 or even the XL50 are great buys, and available at local outdoor/hardware stores. My friend has the XL100, seems a little complex to operate some of the features, I chose the XL50, and at 104 lumens, it is too bright for some work.