Primary 3 Maths | Capacity and Weight (Teacher Lesson Guide)

2026-11-08

Tutor lesson-prep guides · Primary Maths

Almost every lost mark here comes from the unit: 1 L treated as 100 mL, 1 kg as 100 g, or an answer with no unit at all. Build a feel for what 1 L actually is with real containers, then teach the conversion, and 1000 stops looking like a random number.

Objectives — Students can: (1) read a measuring jug and express capacity in L and mL; (2) state that 1 L = 1000 mL and 1 kg = 1000 g and convert between them; (3) add, subtract and compare capacities or weights, writing the correct unit; (4) make sensible estimates for familiar objects, such as a cup of water at about 250 mL or an apple at about 200 g.

01 Prerequisites (3-minute check)

If any of these fails, fix it before the lesson starts.

Skill	Quick check	Pass mark
Three-digit addition and subtraction	What is 750 + 250?	1000
Multiplication	What is 6 x 200?	1200
Comparing numbers	Which is larger, 1200 or 1000?	1200
One decimal place	What does 1.5 mean?	One and five tenths, so 1.5 L is 1 L 500 mL

02 Lesson flow (45 minutes)

Time	Stage	Tutor does	Student does
0-9 min	Entry: pour and feel	A 1 L bottle and a 250 mL cup; pour four cups to fill the bottle	They say four cups make one bottle
9-18 min	Reading a jug	Show where 500, 750 and 1000 sit and what each small division means	They read three water levels in mL
18-27 min	Litres and millilitres	Model 1 L = 1000 mL and 2 L 500 mL = 2500 mL	Six conversions, both directions
27-36 min	Kilograms and grams	Weigh 1 kg of rice and 750 g of apples on a scale	Six conversions plus one estimate
36-43 min	Add, subtract and compare	Model 1 L minus 750 mL leaves 250 mL; compare 1200 g with 1 kg	Five questions, unit written each time
43-45 min	Exit check	Three quick oral questions	Answered independently

03 Teaching script (read it out)

Scene 1: One litre is four cups, not just a number

Students memorise 1000 with no feel for it, then answer that a drinking glass holds 1 L. Anchor it to the most familiar container: an ordinary cup is about 250 mL, so four cups make 1 L, and a 250 mL carton four times over is the same litre.
With that anchor, estimation questions become possible, and absurd answers like “5 mL in a bucket” are visible at a glance.

Student says: the approximate capacity of three objects in the room.

Scene 2: There is one bridge: multiply or divide by 1000

Students treat 1 kg as 100 g because “kilo sounds like a small extra”. Say what kilo means: one thousand. Then fix the direction: bigger unit to smaller unit multiply by 1000, smaller to bigger divide by 1000.
Run L with mL and kg with g through the same rule, together, so students see one rule rather than two sets to memorise.

Student does: writes “x1000” or “/1000” beside every conversion before calculating.

Scene 3: Convert before you add or compare

A question mixes L and mL and the student adds the numbers straight off, landing a factor of a thousand out. Require everything in the smaller unit first, then add or subtract, then write back in the unit the question asks for.
Comparisons work the same way: 1 kg against 1200 g has to be converted first, otherwise “1200 is bigger than 1” appears on the page.

Student does: writes “all in mL” or “all in g” as the first line of every question.

04 Question types and worked steps

Type	Example	Steps	Answer
Reading a jug	Level between 750 and 1000, each small division 50 mL	Read the big mark, then count divisions	850 mL
Conversion	2 L 500 mL to mL; 3 kg to g	Multiply going down, divide going up	2500 mL; 3000 g
Add, subtract, compare	1 L used up by 750 mL; 1200 g against 1 kg	Convert first, then calculate or compare	250 mL left; 1200 g is heavier
Everyday estimate	A cup of water, a bucket, an apple	Anchor on the 250 mL cup and the 1 kg bag of rice	About 250 mL; about 200 g

Sanity check (teach this): Reasonableness checks: every answer has a unit and it matches the question; 1 L is exactly 1000 mL, so 100 or 10 means the conversion broke; capacities must share a unit before adding; estimates must land in a plausible range, since a cup is not 1 L and an apple is not 1 kg; comparisons never compare bare numbers without units.

05 Independent practice (3 questions)

Question	Answer	What to watch
6 conversions	Three L to mL, three kg to g	Checks the direction is not reversed
5 add and subtract questions	Mixed units, two answers required in the larger unit	Checks units were unified first
3 estimates	Judge from a picture whether a capacity or weight is plausible	Checks the answer sits in a sensible range

06 Common mistakes and what to say

Mistake	Student writes	Say this
Treating 1 kg as 100 g	Answer “1 kg = 100 g”	“Kilo means a thousand. 1 kg is 1000 g, the same rule as 1 L being 1000 mL.”
Adding mixed units directly	1 L + 250 mL answered as 251	“Get them into one unit first: 1000 mL plus 250 mL is 1250 mL.”
Dividing the wrong way	2500 mL converted to 2500 L	“Small to big means divide by 1000, so 2500 mL is 2.5 L. It cannot get bigger.”
Estimates far off	Answer “the bucket holds 5 mL”	“5 mL is a teaspoon. A bucket is measured in litres, about 5 L.”

07 Homework (paper, section and question numbers)

Primary 1 to 6 Maths test papers with answers — Do the P3 capacity and weight questions, unit written each time
Primary Maths chapter index — All chapters in the subject
Redo this chapter — Redo six conversions, writing x1000 or /1000 first

08 Exit check (last 5 minutes)

Question	Answer	Decision
How many mL in 1 L	1000 mL	Answering 100 mL means going back to the second stage
How many g in 1 kg	1000 g	Answering 100 g means going back to the fifth stage
What comes before adding mixed units	Convert to one unit	Answering “just add” means going back to the fourth stage
A cup of water is about	250 mL	Answering 1 L means going back to the second stage

09 Tutor FAQ

What if there is no jug or scale?

Use a marked bottle, a medicine cup or the weights printed on supermarket packs. The point is for students to meet 1000 as something real.

Should tonnes be taught?

Not in P3. Secure L with mL and kg with g first, and leave tonnes for upper primary.

How is an estimate marked?

Any plausible range earns the mark, for example 200 to 300 mL for a cup, provided the student says which anchor they used.

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A TutorZone lesson-prep guide. Written by the TutorZone team; questions and lesson flow are original and are not taken from any school or publisher material.