For Castillo, I would compare 柯 Kē for a short sound-linked name and 城 Chéng for a chosen fortification image. 卡 preserves the opening character of 卡斯蒂略, but its surname reading needs care: Shogakukan directly records Qiǎ, while the Kǎ surname reading cited here comes from a secondary surname compilation whose printed sources were not independently inspected. 1, 2, 3, 4, 5
I would not rule out 卡 merely because it is unfamiliar. I would also not describe Kǎ as unanimously established by the stronger dictionary source. Your choice depends on whether you value the original written opening, a simpler reading explanation, or the architectural meaning.
What the full Chinese spelling preserves
The Chinese Ministry of Foreign Affairs pairs Castillo with 卡斯蒂略, while the NAER Spanish surname table uses 卡斯堤悠. Both start with 卡. These are documented forms, not a claim that all Castillo families use the same transcription. 1, 2
A Spanish reference pronunciation places the stress on the middle syllable, ti. The sound represented by ll varies by dialect and family, as the RAE’s account of yeísmo helps explain. Living in the United States or reading English does not establish your preferred pronunciation. 10 Start from the way you introduce yourself, rather than imposing a single American or Spanish reading.
Taking just Kǎ removes the later syllables, including the stressed portion of the Spanish name. The Mandarin k is aspirated and the syllable carries a third tone; neither property simply duplicates Spanish ca-. Keeping the complete transcription retains more of the original name, even though it still adapts the sounds to Mandarin.
The two readings of 卡 are not interchangeable
Shogakukan's Chinese–Japanese dictionary separates kǎ, including foreign-name transcription uses, from qiǎ, whose fourth sense explicitly marks a surname. A general list of two character readings would not prove that both apply to surnames. The subsection matters. 3
Hao86's surname compilation separately states Kǎ as a surname reading and cites surname books; it also gives Qiǎ. This is useful secondary evidence for Kǎ, but the cited printed originals were not independently inspected for this article. It should retain that attribution and limitation. 4
Qiǎ preserves the written character but substantially changes the sound relative to ca-: pinyin q is an aspirated palatal affricate, with the following glide represented by i. Choosing Qiǎ is therefore not an acoustically equivalent way to retain Kǎ. Choosing Kǎ may require saying 我姓卡，读kǎ and accepting the narrower evidence available here.
柯 Kē is independently recorded as a surname by the MOE. It retains an aspirated velar opening but replaces the a vowel with the Mandarin vowel written e, and uses a level first tone. It is a new adaptation, not the initial character of the two Castillo transcriptions checked here. Its wood-related meanings do not make Castillo a carpenter's surname. 5
城 keeps an image rather than the sound
The surname dictionary traces Castillo to residence near a castle or fortified building, or to a place named with that word. It does not establish that every bearer descends from castle owners, nobles or soldiers. 6
The MOE records 城 Chéng both as a surname and as a word for defensive walls or a city. That makes a fortification association possible, but 城 is not a precise equivalent of every European castle. Chéng also gives up most of Castillo's sound. The proposal is an editorial connection between two architectural images. 7
郭 Guō narrows the image to an outer wall. It is independently a surname, but I would add it only if that enclosure is specifically what appeals to you. It does not make the pronunciation closer to Castillo. 8
A personal interest in protection or community can guide the given name later. It is not evidence of a shared Chinese–Spanish lineage, and adopting a character cannot promise courage or social standing.
Try the choice in an introduction
Keep 卡斯蒂略 if recognisability matters more than brevity. Compare 卡 and its explicitly chosen reading when continuity is the priority. Try 柯 when its particular sound and stronger direct reading evidence suit you, or 城 when the fortification image is the point.
Read each finalist before the same proposed given name. Ask someone who has not seen your explanation to read the characters, especially 卡, and check unintended combinations. Retain Castillo alongside the Chinese name in bilingual contexts.
The U.S. figure is historical census data
The U.S. Census row records CASTILLO, rank 94, frequency 231,347. It belongs to the 2020 Census surname tabulation, after disclosure-avoidance processing, released April 14, 2026. It is not a count of current 2026 residents, and it is not added to Spain's separate first-surname count. A statistical spelling cannot determine a person's language, ancestry or name pronunciation. 9
Sources and notes
Chinese MFA Mexico profile The surname transcription is used as lexical evidence, without making a current-office claim.
NAER Spanish surname table Castillo is paired with 卡斯堤悠.
Shogakukan 卡 Surname sense 4 is under qiǎ. The separate kǎ section contains transcription uses.
Hao86 卡 surname Separate Kǎ and Qiǎ surname explanations. This is a secondary compilation; its cited printed books were not independently inspected.
MOE 柯 A direct surname sense under kē.
DAFN Castillo via FamilySearch Attributed to Patrick Hanks 2003, 2006. Habitational or topographic origin, not a universal lineage.
MOE 城 Surname use and defensive-wall/city senses are separately recorded under chéng.
MOE 郭 Surname use and outer-wall sense are separately recorded under guō.
U.S. Census 2020 surnames 2020 reference data released April 14, 2026, with disclosure-avoidance processing.
RAE yeísmo Spanish ll/y variation.
