Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2024	Feb. 07, 2025	Jun. 30, 2024
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2024
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	FY
Trading Symbol	CPTP
Entity Registrant Name	CAPITAL PROPERTIES, INC.
Entity Central Index Key	0000202947
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Shell Company	false
Document Financial Statement Error Correction [Flag]	false
Entity Emerging Growth Company	false
Entity Current Reporting Status	Yes
Entity File Number	001-08499
Entity Tax Identification Number	05-0386287
Entity Address, Address Line One	5 Steeple Street, Unit 303
Entity Address, City or Town	Providence
Entity Address, State or Province	RI
Entity Address, Postal Zip Code	02903
City Area Code	401
Local Phone Number	435-7171
Entity Interactive Data Current	Yes
Document Annual Report	true
Document Transition Report	false
Entity Common Stock, Shares Outstanding		6,599,912
Entity Incorporation, State or Country Code	RI
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Public Float			$ 18,700,000
Title of 12(g) Security	Class A Common Stock, $.01 par value
Auditor Name	Stowe & Degon, LLC
Auditor Location	Westborough, MA, USA
Auditor Firm ID	577
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE Portions of the Company’s Proxy Statement for the 2025 Annual Meeting of Shareholders to be held on April 30, 2025, are incorporated by reference into Part III of this Form 10-K.
Auditor Opinion [Text Block]	Opinion on the Financial Statements We have audited the accompanying consolidated balance sheets of Capital Properties, Inc. (the “Company”) as of December 31, 2024 and 2023, and the related consolidated statements of income and retained earnings, and cash flows for each of the years in the two-year period ended December 31, 2024, and the related notes (collectively referred to as the “consolidated financial statements”). In our opinion, the consolidated financial statements present fairly, in all material respects, the financial position of the Company as of December 31, 2024 and 2023, and the results of its operations and its cash flows for each of the years in the two-year period ended December 31, 2024, in conformity with accounting principles generally accepted in the United States of America.

CAPITAL PROPERTIES INC /RI/ 10-K