Deadbolt Grades Explained: Grade 1, 2, and 3

The short answer

Deadbolt grades explained in one line: Grade 1 is the strongest and longest-lasting, Grade 2 is the solid middle, and Grade 3 is the basic level. The grades come from standards written by BHMA, the Builders Hardware Manufacturers Association, and approved by ANSI, the American National Standards Institute. For an outside door of a house we suggest at least a Grade 2 deadbolt with a 1-inch bolt, set in a strong strike plate. Grade 1 is common on commercial doors and is a good upgrade for any door that has been forced before. In Milwaukee a new deadbolt installation starts at $119.

Who sets the grades

BHMA is a trade association of North American door hardware makers. It writes a family of performance standards, numbered A156, and each one covers one kind of hardware: hinges, knob and lever locks, exit devices, door closers, and so on. ANSI approves them as American National Standards. Deadbolts sold for commercial and general use are graded under the standard for auxiliary locks, A156.36. A separate standard for home deadbolts, A156.40, adds letter ratings, which we explain further down this page.

A grade comes from lab testing. A lock is sent to an independent lab, and it receives a grade only if it passes every test for that grade. The grade belongs to the tested product, not to the brand as a whole, so one brand can sell Grade 1, Grade 2, and Grade 3 deadbolts side by side.

What the tests measure

The tests fall into a few groups, and each grade sets a higher bar in each group.

Cycle tests measure how long the lock lasts. The lock is opened and closed by a machine, over and over, and must still work at the end. BHMA requires a Grade 1 deadbolt to pass 250,000 cycles. For knob and lever locks the numbers are higher: under the standard for bored locks, A156.2, Allegion lists 1,000,000 cycles for Grade 1, 400,000 for Grade 2, and 200,000 for Grade 3.

Strength and security tests measure how well the lock holds up to force. Weights strike the bolt and the cylinder, and pulling and twisting forces are applied to the parts a burglar would attack. Grade 1 locks face the heaviest blows and the most of them.

Operational tests check that the key and the thumb turn work with reasonable force, and finish tests check that the surface resists wear, sweat, and corrosion.

The A, B, and C ratings for home deadbolts

In 2015 BHMA added A156.40, a standard written for deadbolts on houses and apartments. It does not use Grade 1, 2, and 3. Instead, each tested deadbolt gets a letter in three categories:

• Security: how well the lock resists force, such as kicks and blows.
• Durability: how long it keeps working with daily use, including with weight on the door.
• Finish: how well the surface holds up to sun, humidity, salt, and hands.

A is the best rating in each category, then B, then C. A deadbolt rated AAA earned the top rating in all three. These ratings appear on a BHMA label on the package. An A rating does not match any commercial grade exactly, so a residential AAA and a commercial Grade 1 are two different measures. Some deadbolts carry both.

For a front door, the security letter matters most. For a rental with heavy use, durability matters too. For a door that faces the weather, look at finish.

Which grade for which door

• Front and back doors of a house: Grade 2 at least, or an A in security on the residential scale.
• A door that faces an alley, a door that was forced before, or a door out of view from the street: Grade 1.
• The door from the garage into the house: treat it as an outside door.
• Doors in a business, a school, or an apartment building's common areas: Grade 1, because the cycle count runs much higher.
• Interior doors: a deadbolt is rarely needed, and a privacy lock does the job.

Builders and flippers often choose basic locks to keep costs down, so the deadbolt on your door may be a Grade 3 model. If the lock works, a rekey is enough for new keys. If you want more strength, a new deadbolt is the change that adds it.

Reading the box

Look for the words ANSI/BHMA, the standard number, and the grade, for example A156.36 Grade 2, or the BHMA label with three letters. Be careful with wording like equivalent to Grade 1 or meets Grade 1 standards. That wording often means the maker built the lock to resemble a graded one but did not send it for testing. BHMA keeps an online directory of products that passed its tests, and you can look up a model there before you buy.

The grade is only half of a strong door

A Grade 1 deadbolt in a weak frame still makes a weak door. When a door is kicked, the bolt usually holds and the wood around the strike plate splits. Three details matter as much as the grade:

• A bolt that goes 1 inch into the frame, called a 1-inch throw. Many Grade 1 and Grade 2 deadbolts have one.
• A strike plate held by screws about 3 inches long, which reach the wall framing behind the door frame.
• A solid door, because a thin hollow door can break around the lock.

When we install a deadbolt, we check the frame and the strike and add long screws when the old ones are short. Our page on changing locks after a break-in shows what a kicked door looks like.

Replacing a deadbolt on an existing door

Most deadbolts sold in the US fit the same holes: a round hole through the face of the door and a smaller hole in the edge for the bolt. The distance from the edge of the door to the center of the lock, called the backset, is usually 2-3/8 or 2-3/4 inches, and many deadbolts adjust to both. That is why a new deadbolt can often go into the old holes without new drilling.

A door without a deadbolt needs both holes drilled and a mortise cut in the frame for the strike plate. That is why a new installation starts at $119, while a swap in existing holes is a lock change from $99.