Strong magnets can be used for several things, from do-it-yourself crafts, to chemistry projects. A normal strength magnet is strong enough to hold a single piece of paper to the refrigerator. Strong magnets, however, are powerful enough to hold a 1/4-inch thick stack of 3-by-3-inch sticky notes to the refrigerator, or 20 pieces of notebook paper. Scientifically, magnet strength is measured by voltage produced within a magnetic field. Tesla is the unit measure of flux density, found in magnetic fields. A regular magnet measures .001 Tesla, while a strong magnet measures 10 Tesla.
Office Supply Stores
Office supply stores typically carry strong magnets along with their regular-strength ones. Check package labels at stores like Staples, OfficeMax, and Office Depot to find strength levels and durability. You can also phone or search the store's website (Staples.com, OfficeMax.com, OfficeDepot.com) to find out what products they carry before making a trip to the store.
Tool Supply and Hardware Stores
Most tool-supply and hardware stores also carry strong magnets, and can typically be found in the garage supply and workshop supply areas. These magnets are high-powered, and many times capable of holding a 1/4 inch stack of notecards to a refrigerator or filing cabinet.
Arts & Crafts Stores
Arts and crafts stores also offer a wide range of magnetic products. Ask a store associate where strong magnets are located, using the project you're working on to describe the strength you need.
Online retailers like Containerstore.com, Magnet4Less.com and Amazon.com offer magnets in a variety of strengths, and can many times be purchased at lower prices than the average retail selling price. Online tool-supply stores you can research include NorthernTool.com.
Price-compare websites like eBay.com, eCrater.com,and Buy.com offer magnets at very low prices, from a variety of sellers. Always remember to account for shipping costs when purchasing online.