According to international common sense, if you use ordinary numbers+English units, you generally need spaces except for degrees Celsius and%.

Common English units

Length unit: m (meter), cm (centimeter), mm (millimeter)?

Unit of weight: t (ton), kg (kg), g (gram), mg (mg), μg (microgram)?

Unit of volume: kg/m3 (kg/m3), L (liter, capital), mL (milliliter, capital)?

Time unit: d (days), h (hours), min (minutes), s (seconds)?

Area unit: hm2 (hectare), km2 (square kilometer), a (mu)?

PH value of aqueous solution: pH(p in lowercase, H in uppercase)?

Light intensity: lx (lux) or lux(l is lowercase