Mix reagent A (in general the blue bottle in a BCA kit) and reagent B with ratio of A:B=1:20 for enough volume of using.
Pipette working solution into microplate wells (100μl/well)
Add gradient volume of standard protein (2mg/ml) to each well (5 or more) followed by adding of sample protein (5μl/well)
Mix wells thoroughly with pipet.
Cover the plate and incubate at 37°C for 30 minutes.
Cool down the plate to RT.
Measure the absorbance at or near 562 nm in a plate reader.
Make a standard curve using data of standard protein. Calculate concentration of sample protein from the standard curve.