To pile up or accumulate (intransitive); e.g., snow, dust, work, or feelings can build up over time.
昨夜の雪がまだ道路に厚く積もっている。
Last night's snow is still thickly piled on the road.
机の上に書類がどんどん積もっていく。
Papers are piling up on my desk.
長年の不満が積もって、ついには口論になった。
Years of dissatisfaction accumulated and finally led to a quarrel.
To estimate or amount to (transitive use). This use is somewhat formal or archaic; in modern Japanese 見積もる is typically used instead.
被害額は数百万円に積もると報告された（＝見積もられた）。
The damage was reported to amount to several million yen (i.e., was estimated).
工事費はおよそ一千万円と積もっているので、詳細な見積もりが必要だ。
Construction costs are roughly estimated at ten million yen, so a detailed estimate is needed.