You can think of yardage as the answer to one question: how many yards altogether? Not the length of a single piece, but the whole amount counted up — of cloth on a roll, of sail on a boat, of ground a team has taken. The -age ending is doing the adding.
yardage 可以想成在回答一個問題：「加起來總共幾碼？」它問的不是單一一塊有多長，而是整個量：一匹布用掉多少、一艘船張了多少帆、一支球隊往前拿下多少地。-age 這個字尾就像一個計數器，把一碼一碼累積起來變成一個總數。也因為是總數，它多半當不可數用。
From the word’s history
The packet's Wiktionary entry gives the formation directly: yard + -age, where -age (via Old French, from Latin -aticum) forms nouns of amount or charge. That is why the word means a total rather than a single measurement.
packet 附的維基詞典字源直接寫出構成：yard 加上 -age。-age 經古法文來自拉丁文 -āticum，用來造「數量」或「費用」的名詞。這正好說明為什麼 yardage 指的是加總後的量，而不是單獨一次的測量。
Wiktionary, "yardage"
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