Captain Rainboe . . .
I've never heard of anyone having to: "multiply by three, adding 10% and rounding off a little," to convert meters into feet.
If you don't have primary use metric altimeters, or if the company doesn't give you conversion tables, then you can look on the respective Jeppesen en route chart panels which will give you the equivalent metric/feet altitudes/levels, including separate tables for Mainland China, and for the rest of the metric worlds. . . Uzbekistan, Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan. . .etc. It's not really a big deal.
At most major airports QNH is available from ATC when requested. And Jepp approach charts at major airports include the differential QFE/QNH settings, as well as low level boxed metric conversion tables.