Skip to main content

Patent Searching: Welcome

A guide to patent searching for engineering students


Welcome to the Patent Searching Guide!

Do you have an idea for an invention? There are several possible reasons you may want to do a patent search:

  • Patentability - has my invention or similar inventions been patented? (checking "prior art" for "novelty")
  • Freedom to operate - if already existing, has the patent on this invention expired, meaning others are free to manufacture it? 
  • Mining - are there companies who might be willing to manufacture or market my invention?
  • State of the art - what are the most recent patent applications granted in the area of my invention? (to determine existing solutions and potential competitors)

Whatever your reasons, this guide will help you get started.

Go to the US Patents page to learn more about finding U.S. patents.

Go to the Patent Classification page to learn how patent classification systems work.

Go to the Worldwide Patents page to learn how to find patents outside the U.S.


US patents

Free patent search engines

These are the most well-known free sites.

US Patent and Trademark Office

There are three types of US patents: utility, design, and plant. The vast majority of patents are utility patents, which when granted are good for 20 years.

U.S. “patent documents” include both patents (PatFT database) and patent applications (AppFT database). The International Patent Cooperation Treaty requires that both be searched for prior art. 

Patents issued prior to the Internet (and the computer) must be searched in the official patent office sites using the CPC subject classification system; since they are not born-digital they have not been keyword-indexed.

The USPTO recommends starting your search on their site search box, by combining a few words describing your invention with the phrase "CPC scheme," which should bring up the relevant areas of the classification system (see next tab for further information on the CPC system).  

How to read a US patent

A U.S. Patent has three parts.

  1. Cover Page – contains bibliographic and identifying information (patent number, dates, inventors, classifications, abstract)
  2. Specification (disclosure) - contains a description of the invention (title, summary, cross-references, background, description of drawings, description of invention itself)
  3. Claims - contains one or more claims which define the invention and all its components


Patent Classification

Patent classification systems

Patent classification systems are designed for classifying and retrieving technical subject matter such as patents. They are similar to library classification systems like Dewey and Library of Congress.

  • The US Patent Classification System was used for over 100 years.
  • In 2015, the U.S. Patent and Trademark Office completed the transition to the Cooperative Patent Classification (CPC) system, developed jointly with the European Patent Office.
  • The Cooperative Patent Classification scheme is based on the International Patent Classification System (IPC), which was created in 1975 by the European nations who signed the Strasbourg Agreement. 

The top level of the CPC scheme is Section. There are 8 sections: A – Human Necessities, B – Operations & Transporting, C – Chemistry & Metallurgy, D – Textiles, E – Fixed Constructions, F – Mechanical Engineering, G – Physics, and H – Electricity.

  • Next there are Classes, then Subclasses, then Groups, then Subgroups. Classes are numbered 01, 02, etc. Subclasses get capital letters while Groups are again numbered starting with 1.
  • Subgroups are indicated by a slash (/) and then a 2 (or more) digit number. The “top” group in each subclass is “00”. See the box on the right for an example breakdown of a patent number.

Patent classification example

US patent # 13/840,818 "Degradable polymers and method for fracking applications" has this classification: C09K8/68.

C = Chemistry & Metallurgy

C 09 K = Materials for Miscellaneous Applications, not provided for elsewhere

C 09 K 8 = Compositions for drilling of boreholes or wells

C 09 K 8/68 = ...containing organic compounds

Worldwide patents

Expanding your search

A thorough patent search doesn't stop with U.S. patents. You need to search worldwide patent databases as well, such as PatentScope. You should also consider searching European and Asian patents using the links in the boxes below.

European and Commonwealth patents

Asian patents