Kevin Mark Klughart


Patent Attorney / Engineer


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Patent Drawings


USPTO Drafting Standards

The subject of Patent Drawings often comes up in the discussion of the preparation of a patent application.  Patent Applicants should be aware that the USPTO has strict requirements for the form and content of patent drawings and will reject applications which do not conform to their specifications.  Unfortunately, industry standard formats in the mechanical and other arts are not necessarily acceptable to the USPTO.  While many inventors with moderate CAD skills can utilize common tools such as AutoCADŽ and other similar products to generate acceptable drawings, conformance to USPTO drawing specifications must still be followed.  A copy of the USPTO Guide for the Preparation of Patent Drawings [7.5 MB] may be useful in preparing properly formatted drawings for your patent application.

Inventors may also find useful the textbook "The Patent Drawing Book" by Jack Lo and David Pressman (NOLO Press, ISBN 0-87337-378-2, 1997).  While I don't necessarily agree with all of the content of this text, it does provide some additional insight into proper patent drafting practices.

CAD Drafting Tools

While there are a plethora of CAD drafting tools on the market, most inventors are surprised to find that many of these tools in their standard configuration will NOT generate drawings acceptable by the USPTO.  While I can't endorse any one particular product, many of my clients have had success using the CAD drafting tool RFFLOW (available from  This is a relatively inexpensive CAD tool that is very useful in generating drawings for computer and electronic related inventions, as well as organizing other types of non-computer drawings.  This tool has particular use in generating complex flowcharts and system level diagrams associated with computer system/method and business method patents.  As an aid in helping clients integrating this tool into their patent design methodology, I've developed an RFF Template for use with this product.  The combination of this CAD tool and the provided template can provide an acceptable USPTO drawing that also has an aesthetic and appealing look and feel.

In addition to CAD drafting tools such as RFFLOW, I have found the Windows screen capture/image editing tool HyperSnap-DX (available from

General Drawing Guidelines

For those inventors wishing to generate their own drawings, the following general guidelines will be of use:

Use standard 8.5 x 11-inch paper.

Margins should be a minimum of one inch on each edge.

DO NOT USE MINIMUM LINE WIDTHS for any portion of the drawing.  A general rule here is that the drawing should be legible if passed through a fax machine using minimum resolution.

Use "FIG. XX" with XX being the page number as the title for each drawing, and reference the drawings as such within the written specification.  Drawing sheets should be numbered consecutively, starting with "FIG. 1".

PLACE EACH FIGURE ON A SEPARATE SHEET.  This greatly simplifies correction of drawings.

Drawing titles should be in 24-point font, with other drawing identification text (callouts) being in a minimum of 12-point font.

As an aid in organizing the patent application, each part of the invention is identified by a unique callout number, with a line connecting the callout number and the element being referenced in the invention.  To simplify the application (both from an organizing and editing point of view), use four digit callout numbers, with the first two digits of the callout being the page number in which the invention element is first identified.

I generally suggest that the first one or two drawings in the patent application provide a visual example of the PRIOR ART so that the Patent Examiner can easily contrast the differences between the prior art and the claimed invention.  Note that if these drawings are included, they must be identified as PRIOR ART at the bottom of the page.

A general guideline for drawings that I often convey to clients is that "Patent drawings should read like a comic book, and visually display all relevant embodiments of the invention so that the invention can be fully understood visually without reading the written specification."  Remember that the Patent Examiner is under extreme time pressure to process and dispatch patent applications and his/her performance is graded accordingly.  Making the process easier by incorporating good drawings (and a sufficient number of same) make the examination process easier and also provide a rock-solid basis for your claims construction.


Special formatting and content requirements are indicated for PCT patent applications.  Please contact me or another patent attorney for further information on this topic.

Drawing Examples

The above described general guidelines can be seen in the following example drawing:

Here the general principles of drawing numbering are illustrated.  Note the invention elements associated with FIG. 3 all begin with "03" callout numbers.  With respect to generation of flowcharts and the like, the following diagram may be of use as a general guide:

Here each major system flowchart block begins on a separate page, with the flow injection node labeled as step 00 ("0600") and each step of the method/process individually labeled in sequential order, starting with step "01".  In this fashion it is a simple process to convert the flowchart to a step method claim by copying the flowchart text to a document editor and then tagging each line with sequential numbering.

Note that in some circumstances blocks within a flowchart may reference procedures which in turn must be fully described in additional separate flowchart sheets.  For example:

Here the processes (1707) and (1708) will be more fully described in an additional flowchart.


Contact Information:

Kevin Mark Klughart

Registered Patent Attorney, USPTO

3825 Leisure Lane, Denton, TX 76210-5589

tel: 800-353-1211 / 940-320-0580  -  fax 940-320-0581   email  -  web

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