Virtual measuring ruler

What the ruler does

This page shows an object to measure and a ruler you can drag anywhere, or move with the arrow buttons and arrow keys for fine adjustments. In inches, the ruler is 6 inches long with marks for halves and quarters. In centimeters, it is 15 cm long with a mark for every millimeter. The object starts in a random spot, so the child has to move the ruler into place, just as they would on a desk.

To answer, set the whole inches and choose 0, ¼, ½ or ¾, or set the centimeters and millimeters, then press Check. If the answer is not right, the hint depends on what went wrong: whether the 0 is lined up with one end or not. Something new to measure deals another object.

Why practice with a ruler

Measuring looks simple, but it holds several ideas at once: start at zero, not at the end of the ruler; the marks between the numbers are equal parts; and a reading like 3¾ inches is a fraction on a number line. Common Core standard 3.MD.B.4 asks students to measure lengths with rulers marked in halves and fourths of an inch, and 2.MD.A.1 asks them to choose and use tools like rulers. Practicing on screen gives quick feedback on each reading before children measure real objects.

Common mix-ups

• Starting at the end of the ruler. Most rulers have a small gap before the 0 mark, so the object must start at 0, not at the edge.
• Starting at 1. If the object starts at the 1 mark, the reading is 1 too big; subtract 1, or move the ruler.
• Counting the marks instead of the spaces. The length is the number of spaces between marks, not the number of lines.
• Mixing up quarter and half marks. On an inch ruler the half mark is longer than the quarter marks on either side of it.

A 10-minute measuring routine

• Start in inches. Ask the child to point to the 0 on the ruler before dragging it.
• Measure the first object together, saying the whole inches and then the extra quarters.
• Let the child measure two more alone and press Check each time.
• Switch to centimeters. Show that each centimeter has 10 small spaces, the millimeters.
• End by asking the child to estimate the next object's length before measuring it.

Where it fits by grade

• Grade 2: measure length with tools such as rulers (2.MD.A.1) and estimate lengths in inches, feet, centimeters and meters (2.MD.A.3).
• Grade 3: measure lengths using rulers marked with halves and fourths of an inch (3.MD.B.4).
• Grade 4: know the relative sizes of units and convert, such as 1 m = 100 cm (4.MD.A.1).
• England: Year 2 measures length in centimeters and meters with rulers, Year 3 measures in meters, centimeters and millimeters, and Year 5 learns approximate equivalences such as inches and centimeters.

Learning more

Fractions are on Eurekami's skill map, and reading a ruler is fraction practice in disguise. Daily Practice brings skills back when they start to fade, and teachers can print worksheets with answer keys.