calculating calories burned

Twisted_Wrister

I've been trying to figure out how many calories I am burning by walking on my treadmill. I walk @ 4.0mph for 45 minutes. I've checked several websites with calculators and they all give me different answers! Does anyone out there have a trusted website or formula for doing the math?

Of the sites I have visited, I've gotten answers from about 177 calories burned, all the way to 489!