Numerical Tolerance

Numerical tolerance determines whether student answers that are close to the answer key are counted as correct. In WebAssign, numerical tolerance can be set in four different places to override the default numerical tolerance of ±2%.

Note When significant figure checking is turned on, questions that specify significant figures in the answer key use a different tolerance setting than is discussed here.

By default, new assignments do not override the class settings for numerical tolerance. 

Tip To change this default behavior, create an assignment template that overrides the class settings and set it as your default template.

You can set numerical tolerance values for a class, an assignment, or for a specific question on an assignment. These tolerances override each other, the tolerance set in the question code, and the default WebAssign tolerance.

The actual tolerance that is used is the tolerance with the highest priority:

Tolerance type in highest priority order



Set for specific questions in the assignment

Overrides all other tolerances

Set in the assignment or assignment template for the entire assignment

Overrides tolerance set in class settings and question code, and WebAssign default tolerance

Set in class settings

Overrides tolerance set in question code and WebAssign default tolerance

Default class settings do not specify tolerance.

Set in question code

Overrides WebAssign default tolerance

A tolerance of 0 is almost always specified for mathematics textbook questions, textbook questions requiring students to enter fractions, and textbook questions requiring simple computation of integers.
Note Symbolic mode questions that require tolerance must be set in the question code.

WebAssign default tolerance

WebAssign default tolerance of ±2% is used when no other tolerances are set. This is a standard used by many professional scientists and engineers, and ensures that the answer is correct to three significant figures.
Important Changing numerical tolerance settings can result in granting credit for incorrect responses, as in the following examples:
  • When asking about the speed of a relativistic electron, a 1% tolerance would allow students who round a response of 0.99975c up to 1.00c to be marked correct.
  • When asking students to determine the area of a rectangle that is 32.5 m by 3 m, the exact answer of 97.5 m2 is correct, not, for example, 98 m2 or 100 m2.

If you do change numerical tolerance settings, test every question carefully to ensure that your students receive credit for all correct responses and do not receive credit for incorrect responses.

You can set numerical tolerance as a non-negative number of units, or as a percentage of the answer key.

Key value

Tolerance setting

Responses scored as correct


2% (default)



10 units


For questions with multiple parts, any tolerances that you set in the assignment or class settings apply to all parts of the question. Only the question author can set different tolerances for different parts of a multiple-part question.

Best Practice Do not change assignments that your students are already working on. You are likely to cost your students points, submissions, or both. Instead, consider creating a copy of the scheduled assignment and making your changes to the copy.

If you must change a scheduled assignment, notify your students of the change and rescore the assignment. See Rescore Assignments.