MFP/mapmywalk definition of light/med/heavy pack

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Hi all

I like to walk/hike with a loaded pack stuffed with ankle weights up to about 16kg/35lb - I have no idea what this constitutes under the MFP definition of pack weight. I know the calorie burned thing is a guesstimate at best, but even so I'd like to get this right. Mapmywalk gives three choices (light/med/heavy), but defines none of them as far as I can tell - I assume 35lb is medium, approaching heavy? It's certainly heavier than the normal rucksack I'd take on a proper unsimulated hike.

Many thanks!!