SELECT "Metric value" FROM table_39049 WHERE "Ratio" = '1/20'
How big in metric terms is the unit that has a ratio of 1/20?
CREATE TABLE table_39049 (
    "Unit" text,
    "Russian" text,
    "Translation" text,
    "Ratio" text,
    "Cubic inches (exact)" text,
    "Metric value" text,
    "Imperial" text,
    "US Customary" text
)