Ko te DN (Nominal Diameter) te tikanga o te diameter ingoa o te paipa, koinei te toharite o te diameter o waho me te diameter o roto. Ko te uara o te DN = te uara o De -0.5*te uara o te matotoru o te pakitara o te ngongo. Kia mōhio: Ehara tēnei i te diameter o waho, ehara hoki i te diameter o roto.

Me tohu te diameter ingoa "DN" (pērā i te DN15, DN50) mō te wai, ngā paipa maitai tuku hau (paipa maitai piauau, paipa maitai kore-piauau rānei), paipa rino maka, paipa hiato maitai-kirihou me te paipa polyvinyl chloride (PVC), me ētahi atu.

Ko te De (Diameter o Waho) te tikanga o te diameter o waho o te paipa, te paipa PPR, te paipa PE, te diameter o waho o te paipa polypropylene, e tohua ana ki te De, ā, me tohua katoatia kia rite ki te āhua o te diameter o waho * te matotoru o te pakitara, hei tauira De25 × 3.

Ko te D e pā ana ki te diameter o roto o te paipa.

Ko te tikanga, ko te d te whānui o roto o te paipa raima. Ko ngā paipa raima whakapakari (raima rānei), ngā paipa uku, ngā paipa uku ātete-waikawa, ngā tāera rango me ētahi atu paipa, ko te whānui o roto o aua paipa me whakaatu e te whānui o roto o te d (pēnei i te d230, d380, me ētahi atu).

Ko Φ te diameter o tētahi porowhita noa; ka taea hoki te tohu i te diameter o waho o te paipa, engari i tēnei wā me whakareatia ki te matotoru o te pakitara.