Under the Patent Cooperation Treaty (PCT), drawings are required when necessary to understand the invention, and when included, they must satisfy strict physical and formatting standards set out primarily in PCT Rule 11 to ensure clear reproduction and uniform publication across Offices.
Related Resource: Patent Drawing Rules and Guidelines - Utility and Design Applications
Sheet size and margins
PCT drawing sheets must be A4 size (29.7 cm × 21.0 cm), with a maximum usable surface of 26.2 cm × 17.0 cm; frames around the usable area are not permitted. Minimum margins for drawings are: top 2.5 cm, left 2.5 cm, right 1.5 cm, and bottom 1.0 cm, ensuring legibility after reduction and during international publication.
Line quality and legibility
All drawings must be executed in durable, black, dense, uniformly thick lines without color; the graphical clarity must allow reduction to two-thirds size while preserving all details. Cross-sections should use oblique hatching, and any scale—if shown exceptionally—should be represented graphically rather than by verbal indications.
Numbering and labeling
Figures are numbered consecutively in Arabic numerals independent of sheet numbering, and sheets themselves are numbered consecutively. Reference signs used in drawings should match those in the description and claims; where many reference signs are present, it is recommended to include a separate sheet listing the signs and their corresponding features for clarity.
Text and language on drawings
Only indispensable words should appear in drawings, and they must be placed so that a translation can be pasted over without interfering with any lines, facilitating multilingual processing during international phases and national entries. Flow charts and block diagrams are expressly treated as drawings and must adhere to the same presentation rules.
Separate sheets and components
Drawings must be provided on sheets separate from the description, claims, and abstract, as each major part of the international application begins on its own sheet to support standardized reproduction methods used by receiving Offices and the International Bureau.
Color drawings and photographs
The default PCT standard is black-and-white line drawings; while discussions have explored accommodating color drawings and photographs, acceptance remains limited and typically exceptional, with photographs considered only where drawings cannot adequately depict the subject. Applicants should assume black-and-white compliance unless a specific Office indicates otherwise in practice.
When drawings are required or invited
Drawings are required when necessary for understanding the invention; designated Offices may invite applicants to submit drawings after filing, with a reasonable time limit that is not shorter than two months from the date of invitation, preserving procedural fairness across jurisdictions.
Practical compliance tips
Use A4 sheets, respect margins, and avoid frames to meet the 26.2 cm × 17.0 cm usable area limit.
Keep lines uniformly black and dense; verify readability at two-thirds reduction before filing.
Number figures and sheets clearly; align reference signs with the specification and consider a reference sign index sheet for complex drawings.
Treat flowcharts and diagrams as drawings and format them under Rule 11 to avoid objections in the international or national phases.
Adhering to these fundamentals helps ensure smooth international publication, search, and preliminary examination, reducing the risk of formal defects during national phase entries.
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