Basis of Presentation and New Accounting Pronouncements	6 Months Ended
Jun. 30, 2026
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation and New Accounting Pronouncements	Basis of Presentation and New Accounting Pronouncements Basis of Presentation – The accompanying unaudited condensed consolidated financial statements and related disclosures have been prepared in accordance with accounting principles generally accepted in the United States applicable to interim financial information and with the instructions to Form 10-Q and Rule 10-01 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by generally accepted accounting principles for complete financial statements. In the opinion of management, all adjustments considered necessary for a fair presentation of Koppers Holdings Inc.’s and its subsidiaries’ (Koppers, Koppers Holdings, the Company, we or us) financial position and interim results as of and for the periods presented have been included. All such adjustments are of a normal recurring nature unless disclosed otherwise. Because our business is seasonal, results for interim periods are not necessarily indicative of those that may be expected for a full year. The Condensed Consolidated Balance Sheet as of December 31, 2025 has been summarized from the audited balance sheet contained in the Annual Report on Form 10-K as of and for the year ended December 31, 2025. Certain prior period amounts in the condensed consolidated financial statements and notes to the condensed consolidated financial statements have been reclassified to conform to the current period’s presentation. The financial information included herein should be read in conjunction with our audited consolidated financial statements and related notes included in our Annual Report on Form 10-K as of and for the year ended December 31, 2025. New Accounting Pronouncements – In November 2024, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2024-03, Income Statement - Reporting Comprehensive Income (Topic 220): Expense Disaggregation Disclosures. This ASU requires the disaggregation of certain expenses into specific categories, such as purchases of inventory, employee compensation, depreciation and intangible asset amortization. Additionally, the amendments require disclosure of the total amount of selling expenses and an annual disclosure of the definition of selling expenses. ASU No. 2024-03 is effective for fiscal years beginning after December 15, 2026 and for interim periods within fiscal years beginning after December 15, 2027. Early adoption is permitted. The amendments should be applied either prospectively to financial statements issued for reporting periods after the effective date of this ASU or retrospectively to any and all prior periods presented in the financial statements. We are currently evaluating this ASU to determine its impact on our disclosures.

Basis of Presentation – The accompanying unaudited condensed consolidated financial statements and related disclosures have been prepared in accordance with accounting principles generally accepted in the United States applicable to interim financial information and with the instructions to Form 10-Q and Rule 10-01 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by generally accepted accounting principles for complete financial statements. In the opinion of management, all adjustments considered necessary for a fair presentation of Koppers Holdings Inc.’s and its subsidiaries’ (Koppers, Koppers Holdings, the Company, we or us) financial position and interim results as of and for the periods presented have been included. All such adjustments are of a normal recurring nature unless disclosed otherwise. Because our business is seasonal, results for interim periods are not necessarily indicative of those that may be expected for a full year. The Condensed Consolidated Balance Sheet as of December 31, 2025 has been summarized from the audited balance sheet contained in the Annual Report on Form 10-K as of and for the year ended December 31, 2025. Certain prior period amounts in the condensed consolidated financial statements and notes to the condensed consolidated financial statements have been reclassified to conform to the current period’s presentation.

New Accounting Pronouncements – In November 2024, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2024-03, Income Statement - Reporting Comprehensive Income (Topic 220): Expense Disaggregation Disclosures. This ASU requires the disaggregation of certain expenses into specific categories, such as purchases of inventory, employee compensation, depreciation and intangible asset amortization. Additionally, the amendments require disclosure of the total amount of selling expenses and an annual disclosure of the definition of selling expenses. ASU No. 2024-03 is effective for fiscal years beginning after December 15, 2026 and for interim periods within fiscal years beginning after December 15, 2027. Early adoption is permitted. The amendments should be applied either prospectively to financial statements issued for reporting periods after the effective date of this ASU or retrospectively to any and all prior periods presented in the financial statements. We are currently evaluating this ASU to determine its impact on our disclosures.