The weight is 151.6 kg or 334.2 lbs, assuming that your 1/4-inch thick stainless steel plate has a 48-inch width and 96-inch length. To calculate it:
Convert inches to meters:
1/4 in = 0.00635 m, 48 in = 1.2192 m, 96 in = 2.4384 m
Find the plate volume:
0.00635 m × 1.2192 m × 2.4384 m = 0.0189 m³.
Multiply by the density of stainless steel:
0.0189 m³ × 8030 kg/m³ = 151.8 kg.
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