Check Polkadot's docs on the XCM precompile.

import { Instruction } from "../src/Xcm/v5/Instruction/Instruction.sol";
import { Xcm, fromInstructions } from "../src/Xcm/v5/Xcm/Xcm.sol";
import { v5 } from "../src/Xcm/VersionedXcm/VersionedXcm.sol";
import { VersionedXcmCodec } from "../src/Xcm/VersionedXcm/VersionedXcmCodec.sol";
import { Weight } from "../src/Xcm/v5/Weight/Weight.sol";
import { WeightCodec } from "../src/Xcm/v5/Weight/WeightCodec.sol";
import { XCM_PRECOMPILE_ADDRESS, IXcm } from "./IXcm.sol";

contract XcmWeightEstimator {
  IXcm xcmPrecompile = IXcm(XCM_PRECOMPILE_ADDRESS);

  function weighMessage(
    Instruction[] memory instructions
  ) external view returns (Weight memory) {
    Xcm memory xcm = fromInstructions(instructions);
    IXcm.Weight memory weight = xcmPrecompile.weighMessage(
      VersionedXcmCodec.encode(v5(xcm))
    );
    return Weight({ refTime: weight.refTime, proofSize: weight.proofSize });
  }
}