Interval Notation Calculator
Convert between interval notation, inequality notation, and set-builder notation. Calculate interval properties.
This free online interval notation calculator provides instant results with no signup required. All calculations run directly in your browser — your data is never sent to a server. Enter your values below and see results update in real time as you type. Perfect for everyday calculations, homework, or professional use.
Left endpoint of the interval
Right endpoint of the interval
Results
Length of interval
1
Midpoint
0.5
Radius
0.5
How to Use This Calculator
Enter your input values
Fill in all required input fields for the Interval Notation Calculator. Most fields include unit selectors so you can work in your preferred unit system — metric or imperial, whichever matches your problem.
Review your inputs
Double-check that all values are correct and that you have selected the right units for each field. Incorrect units are the most common source of calculation errors and can produce results that are off by factors of 2, 10, or more.
Read the results
The Interval Notation Calculator instantly computes the output and displays results with units clearly labeled. All calculations happen in your browser — no loading time and no data sent to a server.
Explore parameter sensitivity
Try adjusting individual input values to see how the output changes. This is a quick and effective way to develop intuition about how different parameters influence the result and to identify which inputs have the largest effect.
When to Use This Calculator
- •Use the Interval Notation Calculator when you need a quick mathematical result without writing out all the steps manually, saving time on repetitive calculations.
- •Use it to verify hand calculations on tests or assignments and catch arithmetic mistakes.
- •Use it when teaching or explaining mathematical concepts to others, demonstrating how changing inputs affects the result.
- •Use it to explore the behavior of mathematical functions across a range of inputs.
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About Interval Notation Calculator
The Interval Notation Calculator works with intervals on the real number line, converting between different representations and computing key properties. Interval notation is a concise way to describe sets of real numbers, using brackets [ ] for included endpoints and parentheses ( ) for excluded endpoints. This notation is essential in calculus (domains, ranges, continuity intervals), analysis (open and closed sets), optimization (feasible regions), and probability (continuous distributions). The calculator computes the interval's length, midpoint, and radius, and helps translate between interval notation (like [2, 5)), inequality notation (like 2 ≤ x < 5), and set-builder notation (like {x | 2 ≤ x < 5}). Understanding intervals is foundational for working with functions, solving inequalities, and studying topology.
The Math Behind It
Formula Reference
Interval Notation
[a, b] or (a, b) or [a, b) or (a, b]
Variables: [ ] = included (closed), ( ) = excluded (open)
Absolute Value Form
|x - m| ≤ r ↔ [m-r, m+r]
Variables: m = midpoint, r = radius
Worked Examples
Example 1: Convert inequality to interval
Express -3 < x ≤ 7 in interval notation
(-3, 7], length = 10, midpoint = 2
Example 2: Absolute value to interval
Express |x - 4| ≤ 3 as an interval
[1, 7]
Common Mistakes & Tips
- !Using brackets [ ] with infinity: always write (-∞, a) or (b, ∞) with parentheses at infinity
- !Confusing open and closed: < and > use parentheses ( ), while ≤ and ≥ use brackets [ ]
- !Writing the bounds in wrong order: always lower bound first, upper bound second
- !Forgetting that a single point {a} can be written as [a, a] (a degenerate interval)
Related Concepts
Used in These Calculators
Calculators that build on or apply the concepts from this page:
Frequently Asked Questions
What is the difference between (a, b) as an interval and as a point?
Context determines the meaning. In interval notation, (a, b) represents all numbers between a and b. As an ordered pair, (a, b) represents a point in the coordinate plane. The context of the problem (number line vs. coordinate plane) clarifies which is intended.
Can intervals contain a single point?
Yes. The degenerate interval [a, a] = {a} contains exactly one point. The empty interval (a, a) = {} contains no points. Half-open intervals [a, a) and (a, a] are also empty.
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