Long And Short

What is Length?
Length is the measure of how long or short something is. It tells us the distance between two points. In everyday life we use length to compare objects (which is longer/shorter) and to measure how much space an object takes in one direction.

Standard units of length (metric system)
We use the metric units: millimetre (mm), centimetre (cm), metre (m) and kilometre (km). These units are related by simple conversion steps:

• 10 mm = 1 cm
• 100 cm = 1 m
• 1000 m = 1 km

How to measure

• Use a ruler for small objects (mm, cm). Place the zero mark of the ruler at one end of the object. Read the mark at the other end. Keep your eye straight above the mark to avoid parallax error.
• Use a measuring tape or metre scale for larger objects (m). For very long distances (roads, between towns) use km.
• For curved or irregular objects (a rope, the edge of a shoe), place a string along the curve, mark the length on the string, then straighten the string and measure it on a ruler.
• Always note the unit used. If needed, convert units before adding or comparing lengths.

Why conversions matter
To add, subtract or compare lengths the measures must be in the same unit. For example, add 1 m 25 cm + 75 cm: first convert 1 m 25 cm = 125 cm, then 125 cm + 75 cm = 200 cm = 2 m.

Practical tips for Class 4 students

• Start measuring from the 0 mark on the ruler, not from the end if the ruler end is damaged.
• Round the smaller divisions when you cannot read them exactly (for instance to the nearest mm or nearest cm as asked).
• Use estimation first: is the object closer to 5 cm or 6 cm? Then measure to check.

What are non-standard units? Non-standard units are everyday objects or simple counts used to measure length, area, volume or time when standard units (cm, m, l, s) are not used. Examples: paper clips, hand spans, footsteps, cubes or tiles, claps or heartbeats.

How to measure using non-standard units

• Choose one object as the unit (for example, one paper clip).
• Place the units side by side from one end of the object to the other (no gaps, no overlaps) and count how many units fit.
• If part of a unit remains, record it as a fraction or say ‘about half’ etc.
• Always use the same non-standard unit when comparing lengths of different objects.

Rules and tips

• Use consistent units for fair comparison (all in paper clips or all in footsteps).
• Start measuring from one fixed end and keep units straight and touching.
• Non-standard measurement is good for estimation and learning measurement ideas but not precise. For exact work, use standard units.

When to use them They are great in the classroom for hands-on learning: measuring pencils with cubes, desks with hand spans, area with square tiles, or short intervals of time by clapping.

What is length? Length tells us how long or short an object is. We use measurements to compare and record lengths. To communicate measurements clearly we use standard units of length.

SI (metric) units used in everyday life:

• Millimetre (mm) — very small lengths (thickness of a pencil, a paper edge).
• Centimetre (cm) — small objects (width of a book, length of a pencil).
• Metre (m) — everyday lengths (height of a door, length of a table). Metre is the standard unit of length in the SI system.
• Kilometre (km) — large distances (distance between towns).

Why standard units? If everyone uses the same units we can compare, add and subtract lengths correctly. For example, saying "5 m" has the same meaning everywhere.

How to choose a unit: Use a small unit (mm or cm) for small objects and a larger unit (m or km) for big objects. When adding or comparing lengths, first convert them to the same unit.

Measuring tools: Ruler or scale (cm and mm), measuring tape (m and cm), metre stick, kilometre markers for roads.

What are measuring tools? Measuring tools are instruments used to find how long, tall or short an object is. They give a number (a measurement) with a unit such as millimetre (mm), centimetre (cm), metre (m) or kilometre (km).

Common measuring tools for length:

• Ruler (30 cm scale): Used for short straight objects like pencils and books. Markings are usually in cm and mm.
• Measuring tape: A flexible tape used for measuring longer or curved objects (cloth, body height, door frame). It has cm and mm markings and is useful for metres-long distances.
• Metre stick / measuring rod: A rigid stick exactly 1 m long, used for longer straight lengths indoors or in school.
• Measuring wheel (odometer): For outdoor longer distances (playground, path). The wheel rolls and counts metres.

How to measure correctly (simple steps):

• Place the tool so its 0 mark lines up with one end of the object.
• Keep the tool straight along the object. For curved items use a flexible tape and follow the curve.
• Read the mark at the other end of the object. If the end is between two marks, estimate to the nearest smaller unit (for example nearest mm or half cm).
• Write the number and unit (for example 23 cm).

Things to remember: Always start from the 0 mark. Use the correct unit. Use a flexible tape for curves and a ruler or metre stick for straight edges. For long outdoor distances, count steps or use a measuring wheel and then convert to metres.

What is a scale? A scale (ruler) is a tool used to measure length. It has marks (divisions) that show units such as centimetres (cm) and millimetres (mm). The longer numbered marks usually show centimetres; the small marks between them show millimetres.

Parts to notice:

• Zero point: Start measuring from the 0 mark on the scale.
• Main marks: The numbered marks (1, 2, 3…) represent centimetres.
• Small marks: There are 10 small marks between two cm marks. Each small mark = 1 millimetre (1 mm).

How to read a scale (step-by-step):

1. Place the object so one end is exactly at the 0 mark. If you cannot place it at 0, use the difference method (see below).
2. Look at the other end of the object. First read the last full centimetre mark it has passed.
3. Count the small marks after that centimetre mark up to the object's end — this gives extra millimetres.
4. Write the length as “x cm y mm” (or convert to decimal centimetres: x + y/10 cm).

Difference method (when object does not start at 0): Note the reading at the start and at the end, then subtract: length = end reading − start reading.

How to estimate: If the end falls between two small marks, estimate to the nearest millimetre or half-millimetre depending on how fine the scale is. For Class 4, nearest mm is fine.

What is Measuring Procedure?

Measuring procedure is the step-by-step way we use measuring tools (ruler, tape, metre stick) to find how long, tall or wide an object is using standard units such as millimetre (mm), centimetre (cm) and metre (m).

Tools you will use: ruler (cm and mm marks), measuring tape or metre stick.

Step-by-step procedure

1. Choose a suitable unit and tool (use ruler for small objects, tape or metre stick for larger distances).
2. Place the object on a flat surface and keep the tool straight along the object.
3. Align the zero mark of the ruler/tape exactly with one end of the object. (Do not start from the end of the ruler if the zero is worn; use the true zero mark.)
4. Hold the tool steady and look straight above the other end of the object (eye level) to avoid parallax error.
5. Read the nearest whole number on the scale and then the smaller divisions (e.g., mm) to get an exact reading. If the end lies between two marks, estimate to the nearest half division if required.
6. For objects longer than the ruler, mark the point where the ruler ends on the object, move the ruler forward keeping it straight, and continue measuring. Add the parts to get the total length.
7. Record the length with the correct unit and, if needed, convert to another unit (for example, change 150 cm to 1 m 50 cm or 1.50 m).

Important tips

• Always use standard units (mm, cm, m) so measurements are understandable to others.
• Keep the measuring tool straight and the object steady.
• Read the scale at eye level to avoid mistakes.
• If a measurement falls between two small marks, estimate carefully (e.g., half a centimetre = 0.5 cm = 5 mm).

Common mistakes to avoid: starting from a worn end of the ruler, reading at an angle, ignoring the smallest divisions, and forgetting to add repeated segments for long objects.

What are metre and centimetre? A metre (m) and a centimetre (cm) are units used to measure length. One metre is longer than one centimetre.

Basic fact: 1 metre = 100 centimetres. This is the key to converting between the two units.

How to convert metres to centimetres — multiply by 100 because there are 100 cm in 1 m.
For example: 2 m = 2 × 100 cm = 200 cm.

How to convert centimetres to metres — divide by 100. You can give the answer as a decimal in metres or as metres and remaining centimetres.

Two common methods for cm → m:

• Decimal metres: divide the number of centimetres by 100. Example: 250 cm = 250 ÷ 100 = 2.5 m.
• Mixed units (metres and centimetres): use whole number division by 100. Example: 345 cm = 345 ÷ 100 = 3 metres and remainder 45 cm → 3 m 45 cm.

Tips and checks: If you multiply metres by 100 the result should be larger (more centimetres). If you convert centimetres to metres, the numeric value becomes smaller (because metres are larger units). Always remember 100 cm = 1 m.

What it means: Comparing lengths is finding out which object is longer, shorter or whether two objects are equal in length. Ordering lengths means arranging several objects from shortest to longest (ascending) or longest to shortest (descending).

Ways to compare lengths:

• Direct comparison: Place two objects with one end aligned. The one that extends farther is longer.
• Using a ruler or measuring tape: Measure each object in the same unit (for example, centimetres) and then compare the numbers.
• Conversion before comparing: If measurements use different units (metres and centimetres), convert them to the same unit first, then compare.

Rules and tips:

• Always align one end of the objects when comparing directly.
• Use the same unit for all measurements before comparing (e.g., convert metres to centimetres).
• Use > (greater than), < (less than) and = (equal to) signs to compare numbers.
• To order more than two lengths, convert them to the same unit, write their numeric values, then sort those numbers.

CBSE Class-4 focus: Use centimetres (cm) and metres (m) mainly. Understand simple conversions and practise arranging 3–5 objects by length using direct comparison and measuring tools.

What is estimation of length?
Estimation of length means giving a close or approximate value for how long something is, without measuring it exactly. It helps us save time and gives a quick idea of size.

Units used
Common units for Class 4: millimetre (mm), centimetre (cm) and metre (m). Choose a unit that matches the object’s size (use cm for small objects, m for rooms or long ropes).

Methods to estimate

• Use known references: compare with familiar objects (a pencil ≈ 15 cm, a notebook ≈ 25 cm, a handspan ≈ 20 cm).
• Use a ruler or tape and round the exact measurement to the nearest convenient unit (nearest cm or nearest m).
• Use a number line to see which unit mark the length is closest to and then round.

Rounding rule (how to decide)
When you have a measurement with a fraction of a unit, compare the fraction to half the unit:
If the extra part is less than half the unit → round down. If it is half or more → round up.

Example of the process
If a pencil measures 14.7 cm on a ruler, look at the decimal part (.7). Since .7 ≥ 0.5, round up to 15 cm. If a book is 23.3 cm, .3 < 0.5 so round down to 23 cm.

Tips for good estimation
Measure a few objects to learn common reference sizes, practice rounding on a number line, and choose the unit that makes the estimate easiest and most meaningful.

What it means
Addition and subtraction of lengths means joining or removing parts of measured lengths. To add or subtract lengths correctly, the measures must be in the same unit (for example, both in metres or both in centimetres). If they are not, convert them to the same unit first.

Important units and conversions

• 1 metre (m) = 100 centimetres (cm)
• 1 centimetre (cm) = 10 millimetres (mm)

Steps to add or subtract lengths

1. Make sure all lengths are in the same unit. Convert if needed (for Class 4, usually between m and cm or cm and mm).
2. Write the lengths one below the other, lining up the same units (e.g., metres under metres, centimetres under centimetres).
3. Add or subtract starting from the smallest unit (cm or mm). If the sum of the smaller units reaches the next unit (e.g., 100 cm = 1 m or 10 mm = 1 cm), carry over when adding or borrow when subtracting.
4. Write the final answer in correct mixed units (for example, metres and centimetres).

Worked examples

Example 1 — Addition (metres and centimetres)
Add 1 m 25 cm and 2 m 80 cm.

1. Add the centimetres: 25 cm + 80 cm = 105 cm.
2. Convert 105 cm = 1 m 5 cm.
3. Add the metres: 1 m + 2 m + 1 m (carried) = 4 m.
4. Answer: 4 m 5 cm.

Example 2 — Subtraction (metres and centimetres)
Subtract 1 m 80 cm from 3 m 15 cm.

1. We cannot subtract 80 cm from 15 cm, so borrow 1 m (100 cm) from 3 m: 3 m 15 cm = 2 m 115 cm.
2. Now subtract centimetres: 115 cm − 80 cm = 35 cm.
3. Subtract metres: 2 m − 1 m = 1 m.
4. Answer: 1 m 35 cm.

Example 3 — Addition (centimetres and millimetres)
Add 45 cm 7 mm and 12 cm 9 mm.

1. Add millimetres: 7 mm + 9 mm = 16 mm. Since 10 mm = 1 cm, 16 mm = 1 cm 6 mm.
2. Add centimetres: 45 cm + 12 cm + 1 cm (carried) = 58 cm.
3. Answer: 58 cm 6 mm.

Tips for students

• Always check units first. Convert before performing the operation.
• Line up the units in columns (m | cm or cm | mm).
• Use a ruler or tape measure to check answers with real objects.

What is a line of given length?

A line of given length is a straight line segment whose two end points are at a specified distance apart (for example 4 cm, 7.5 cm or 15 mm). In Class 4 we learn to draw such line segments accurately using simple tools: a ruler (scale), pencil and sometimes a compass or divider.

Tools and units

• Ruler (with centimetre and millimetre marks)
• Pencil and eraser
• Compass or divider (optional for transferring lengths)
• Units: 1 cm = 10 mm, 1 m = 100 cm. Small lengths are usually measured in centimetres (cm) and millimetres (mm).

Step-by-step method using a ruler

1. Decide the required length, for example 6 cm.
2. On your paper, mark the first end point and name it A.
3. Place the ruler so that the 0 mark of the ruler is exactly at A.
4. Find the required length mark (for 6 cm, find 6 on the ruler) and make a small mark there; name it B.
5. Remove the ruler and join A and B with a straight pencil line. The segment AB is the required line of that length.

Method using a compass (to transfer length)

1. Draw or mark a short segment on the ruler or another piece of paper with the required length (or measure an existing segment AB).
2. Open the compass so that the distance between its points equals the required length.
3. Place one point of the compass at the starting point on your drawing and mark the second point with the pencil end; join the two points to get the line segment.

Tips for accuracy

• Always start measuring from the 0 mark on the ruler, not from the end if the ruler end is worn.
• Keep your eye straight above the mark to avoid parallax error.
• Use the mm marks for more precise lengths or for halves and decimals (for example 7.5 cm = 7 cm 5 mm).

What are word problems? Word problems are math questions written in sentences that use real-life situations. They ask us to read, understand, and use maths (like addition, subtraction, multiplication, division, and measurement) to find an answer.

How to solve word problems about length (Long and Short)

1. Read carefully: Find what is asked and what data are given (lengths, number of items, units).
2. Draw or model: Use a simple picture, a ruler sketch or a bar model (strip diagram) to show the situation.
3. Choose the operation: Decide whether to add, subtract, multiply, or divide.
4. Convert units if needed: Make sure all lengths use the same unit (cm, m, mm or km) before calculating.
5. Calculate: Do the arithmetic. For lengths, remember to carry or borrow between units (100 cm = 1 m, 10 mm = 1 cm).
6. Check your answer: See if the answer makes sense in the story (reasonable size, correct units).

Important ideas for Class 4 (Lengths)

• Units and conversions: 1 m = 100 cm, 1 m = 1000 mm, 1 cm = 10 mm, 1 km = 1000 m.
• Addition/subtraction of lengths: add metres with metres and centimetres with centimetres; if centimetres ≥ 100, convert to metres and centimetres.
• Multiplication/division with lengths: multiply when many equal pieces are joined; divide when a length is shared equally.
• Use simple formulas like perimeter of a rectangle = 2 × (length + breadth) when needed for fencing or borders.

Real-life examples include measuring ribbon, adding lengths of wood, finding how much cloth is left after cutting, finding total distance travelled by repeating a walk, or deciding how much fence is needed around a rectangular garden.