What size metric wire is required for 240 VAC 30 Amps located in house with run of 90M or <100 feet to a garage
In the US, a 30 ampere circuit would use 10 AWG conductors.  10 AWG is 5.261 mm². However, if you're going 90 meters (295 feet), you might have to compensate for voltage drop. You might go up to 8 AWG (8.367 mm²), or possibly even 6 AWG (13.3 mm²).

These figures are based on codes in the US, so you'll have to check local codes before proceeding.

EngineeringToolbox.com has a good conversation chart to go from AWG to mm².