Create customizable number lines with tick marks, labels, fractions, and highlighted intervals for math education.
The guide
This tool draws a horizontal number line to your specifications: a start and end value, a tick spacing, and what to write under the ticks - integers, decimals, fractions, or nothing. You can also mark one or more intervals with a colored band, and the finished line renders as a graphic, ready to print or drop into a worksheet. The thing people most often misjudge is the off-by-one: a setting that asks for a tick count usually means intervals, so ten ticks produce eleven marks. And a fraction label lands exactly on a tick only when the fraction is a whole multiple of the step you chose.
A concrete input and expected output from the current implementation.
Input
Line from -1 to 1, tick every 0.25, label every 4th tick as a decimal, highlight the interval from -0.5 to 0.5
Expected output
A horizontal number line with nine ticks at -1, -0.75, -0.5, -0.25, 0, 0.25, 0.5, 0.75, 1; labels under -1, 0, and 1 only; and a filled band covering the four intervals between -0.5 and 0.5.
The range is 2 units wide and the step is 0.25, so the line holds 8 intervals and 9 ticks. The band starts at the third tick and ends at the seventh, covering 4 of the 8 intervals, exactly half the line.
Minimum, maximum, and step define the line. Ticks sit at every multiple of the step within the range, so the tick count is (max - min) / step + 1. Each tick's position is its share of the range, (value - min) / (max - min), as a fraction of total width. When the step does not divide the range evenly, the last interval falls short and the endpoint is not a tick.
Labels can be integers, decimals, or fractions. A fraction label is placed at its decimal value, so it sits exactly on a tick only when the fraction is a whole multiple of the step; otherwise it falls between ticks. Highlighted intervals render as a colored band between two values, with edges on the nearest ticks. A label-every-Nth-tick option keeps dense lines readable.
Yes. The range simply starts below zero, for example -5 to 5, and the same tick math applies. One practical point: label zero when the line crosses it, because students read the negative side by counting away from zero. A line with negative ticks but no labeled zero is easy to misread, so set the label interval so that zero falls on a labeled tick.
Because the label is placed at its decimal value, and it lands on a mark only when that value is an exact multiple of the step. One-third on a tenths-stepped line has the value 0.333..., which sits between the 0.3 and 0.4 ticks. Choose a step the denominator divides evenly, such as twelfths for thirds, or accept the off-tick position.
The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.
