how to calculate worm gear ratio

{"cid":"91212205","title":"Helical Gear Worm Gear Reducer Gear Box 3600 RPM Speed Reduction","imgUrl":"https:\/\/img.silkroadsl.com\/nimg\/7c\/e7\/3aebee3c3468589dd35bcafba4d3-200x200-1.jpg","attrs":{"Price":"$1000\/ Set","Brand Name":"YIZGEAR","Model Number":"GB22080803","Minimum Order Quantity":"1 Set","Delivery Time":"55 Days","Place of Origin":"CHINA","Payment Terms":"L\/C, T\/T, Western Union, D\/P","Supply Ability":"150 Sets\/Month","Packaging Details":"Plywood Crate","Material":"20CrNiMo","Profile Type":"Helical Gear\/ Worm Gear","Weight":"47 KG","Type":"Three Stage","Color":"Orange","Rated RPM":"3600"}}

{"cid":"91189141","title":"Japanese ISUZU NKR Truck 8\/41 Crown Wheel Pinion","imgUrl":"https:\/\/img.silkroadsl.com\/nimg\/8c\/37\/ed9c30f2af34013f72f848d68d48-200x200-1.jpg","attrs":{"Price":"Negotiable","Brand Name":"Isuzu","Model Number":"Isuzu 700P NPR","Minimum Order Quantity":"1","Delivery Time":"5-8 DAYS","Certifiion":"ISO9001\/TS16949","Place of Origin":"China","Payment Terms":"L\/C, D\/A, D\/P, T\/T, Western Union, MoneyGram","Supply Ability":"1000 PCS PER WEEK","Packaging Details":"CARTON BOX","Product name":"ISUZU NKR 8\/41 Crown Wheel Pinion","Car model":"Isuzu","Warranty":"12 month","Condition":"Brand new and good condition","Material":"steel","Packing":"Neutral packing"}}