When it comes to forwarding a parcel, the total number of the width, the length and the height under 60 cm costs you less expensive than under 80 cm.
"荷物の縦・横・高さの合計が60㎝以下"
～する段になると when it comes to ~ （toは前置詞なので後ろは名詞、名詞形）
When it comes to forwarding a parcel, the total number of the width, the length and the height under 60 cm costs you less expensive than under 80 cm.
日本 
