16GB DDR4 ECC 2933MHz R-DIMM — two 8GB DIMMs.
32GB DDR4 ECC 2933MHz R-DIMM — two 16GB DIMMs.
64GB DDR4 ECC 2933MHz R-DIMM — two 32GB DIMMs.
128GB DDR4 ECC 2933MHz LR-DIMM — two 64GB DIMMs.
256GB DDR4 ECC 2933MHz LR-DIMM — two 128GB DIMMs.
Note: R-DIMMs and LR-DIMMs cannot be used in the same system; all DIMMs in Mac Pro (2019) must match.