六百(ろっぴゃく)

六(ろく) + 百(ひゃく), pronounced ろっぴゃく. Learners often say the regular ろくひゃく by mistake; the doubled consonant and the p-sound are both required.

Sound changes in the hundreds

• 三百(さんびゃく): ひゃく → びゃく
• 六百(ろっぴゃく): ろく → ろっ, ひゃく → ぴゃく
• 八百(はっぴゃく): はち → はっ, ひゃく → ぴゃく

The rest — 四百(よんひゃく), 五百(ごひゃく), 七百(ななひゃく), 九百(きゅうひゃく) — are regular.

Similar patterns

The same ろっ appears before other h-initial counters: 六匹(ろっぴき), 六本(ろっぽん), 六分(ろっぷん).