Weights I've seen quoted for the bronze muscle cuirasses (both plates, mind you) are in the 30 pound range. Which sounds credible enough; AFAIK most decent-coverage mail shirts weigh about the same (although there can be very considerable variation due to "cut" alone), and good steel breastplates rather a bit less. (Early Modern "proof" cuirasses, with double-thick 4mm front plate, are about 25-30 pounds; normal-thickness ones about 75% of that.) 'Course, exact coverage, design, thickness and such can vary the figures quite a bit.
Not that it really matters. Medieval knights fighting dismounted could cheerfully be wearing full mail, a coat-of-plates over it for serious torso protection (and neither armour is exactly light by itself), plus helmet and sundry additional limb defences plus weapons, and normally didn't have too much trouble with the load. They didn't cover ground all that fast of course, but then if they needed to be mobile they'd stay on horseback to begin with.
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