Telling time to the minute, mass, and volume
Reading a clock to the minute, elapsed time, and measuring mass and liquid volume
About three lessons of 45 to 60 minutes
Every day runs on time, mass, and volume
You already read a clock, you already know a big bag of flour is heavier than a small one, and you already know a big cup holds more juice than a small one. This unit gives those everyday judgements exact numbers: minutes on a clock face, grams and kilograms on a scale, millilitres and litres in a jug.
The three ideas share one habit of mind: read the scale carefully, then use the count you read to answer a real question, like how long a movie lasts or how much milk is left in the jug.
- The minute hand between the 4 and the 5count on in ones from the last five-minute mark: 23 minutes past
- A movie that starts at 2:45 and ends at 4:10elapsed time, counted on in friendly jumps
- A bag of apples with a mass of 2 kg 300 g1 kilogram is 1000 grams, so that is 2300 g altogether
- A jug that holds 1 L 250 mL of juice1 litre is 1000 millilitres, so that is 1250 mL altogether
What students will be able to do
Students will tell time to the nearest minute, find elapsed time by counting on in friendly jumps, and measure, estimate, and solve one-step word problems involving mass (grams and kilograms) and liquid volume (millilitres and litres).
- I can read an analog clock to the exact minute.
- I can find how much time has passed between a start time and an end time by counting on.
- I can convert between kilograms and grams, and between litres and millilitres.
- I can solve a one-step word problem about mass or volume.
Standards this unit teaches
- 3.MD.A.1Common Core (US)Time intervals to the minute
Tell time to the minute and solve word problems about elapsed time intervals.
- 3.MD.A.2Common Core (US)Mass and volume
Measure and estimate liquid volumes and masses of objects and solve one step problems involving them.
- AC9M3M03Australian Curriculum v9 (ACARA)Time, am and pm
Solve problems about how long things take, including situations with am and pm and converting between units of time.
- AC9M3M01Australian Curriculum v9 (ACARA)Read scales and units
Read scaled and digital instruments to measure and compare length, mass, capacity, duration and temperature, including partial units.
Prior knowledge
This unit builds on skills students should already have met. Revisit any that are shaky first.
Words to teach and display
- Elapsed time
- how much time has passed between a start time and an end time
- Mass
- how heavy something is, measured in grams and kilograms
- Volume (capacity)
- how much liquid something holds, measured in millilitres and litres
- Kilogram
- a unit of mass equal to 1000 grams
- Litre
- a unit of liquid volume equal to 1000 millilitres
Teach it: concrete, pictorial, abstract
The lesson moves from things students can hold, to pictures and diagrams, to the written maths. The diagrams below are drawn from data, so they are accurate and print cleanly. Teach straight from them.
1. Telling time to the minute
ConcreteThe hour hand is short and slow, the minute hand is long and fast. Find the hour first from where the short hand points (between two numbers means that hour has started but not finished). Then read the minute hand: count on in fives from the 12 to the nearest five-minute mark the hand has passed, then count on in ones to the exact minute.
This two-step count (fives, then ones) is the whole skill. A minute hand sitting exactly on a number is easy: on the 4 is 20 minutes. A minute hand between numbers needs the extra one-by-one count past that mark.
The hour hand is between the 3 and the 4. The minute hand has just passed the 4 and sits three small marks further on. What time is it?
- The hour hand is between 3 and 4, so the hour is still 3 (it has not reached 4 yet).
- Count on in fives to the 4: 5, 10, 15, 20 minutes.
- The hand is three small marks past the 4, so count on three more ones: 21, 22, 23.
- 20 plus 3 is 23 minutes.
Answer: The time is 3:23.
- Which hand do you check first to find the hour?
- The minute hand is exactly on the 7. How many minutes is that, and how did you get it without counting by ones the whole way?
2. Elapsed time: counting on in friendly jumps
PictorialNever subtract clock times like ordinary column subtraction. A clock runs in groups of 60, not groups of 10, so borrowing goes wrong. Instead count on from the start time to the end time in friendly jumps: first to the next o'clock, then in whole hours, then the leftover minutes.
A movie starts at 2:45pm and ends at 4:10pm. How long is the movie?
- Jump from 2:45 to the next o'clock, 3:00: that is 15 minutes.
- Jump from 3:00 to 4:00: that is a whole hour, 60 minutes.
- Jump from 4:00 to the end time, 4:10: that is 10 minutes.
- Add the jumps: 15 + 60 + 10 = 85 minutes.
- 85 minutes is 60 minutes plus 25 minutes, so 1 hour 25 minutes.
Answer: The movie is 1 hour 25 minutes long (85 minutes).
- Why is counting on in jumps safer here than subtracting the times like ordinary numbers?
- What is the first jump you would make from 9:50am to find elapsed time to 11:15am?
3. Mass and volume: units, estimating, and word problems
AbstractMass tells you how heavy something is (grams and kilograms); volume tells you how much liquid it holds (millilitres and litres). Both systems work the same way: 1000 of the small unit makes one of the big unit, so kilogram is to gram as litre is to millilitre.
To go from the big unit to the small unit (kg to g, or L to mL), there will be more of the smaller unit, so multiply by 1000. To go the other way, there will be fewer of the bigger unit, so divide by 1000.
Estimating first, before measuring on a real scale or jug, catches silly answers: a bag of apples having a mass of 2300 kg (heavier than a car) should immediately look wrong.
A recipe uses a jug with 1 L 250 mL of juice already in it, then two more 200 mL cups are poured in. How much juice is in the jug now, in millilitres and then in litres and millilitres?
- Convert the starting amount to millilitres: 1 L 250 mL = 1000 mL + 250 mL = 1250 mL.
- Add the two 200 mL cups: 200 + 200 = 400 mL.
- Total: 1250 + 400 = 1650 mL.
- Convert back: 1650 mL = 1000 mL + 650 mL = 1 L 650 mL.
Answer: The jug now holds 1650 mL, which is 1 L 650 mL.
- A pumpkin has a mass of 3 kg. A watermelon has a mass of 4500 g. Which is heavier, and by how much?
- Why do we multiply by 1000 to go from kilograms to grams, but divide by 1000 to go the other way?
Common misconceptions and how to address them
MisconceptionThe long, fast-moving hand tells the hour and the short hand tells the minutes, or the two get mixed up under time pressure.
Why it happens: Nothing about the hands' appearance obviously signals which is which until it is taught explicitly, and the minute hand's constant motion draws the eye first.
How to address it: Say the rule every time: short and slow is the hour, long and fast is the minute. Cover one hand at a time on a teaching clock so students commit to reading the short hand first.
MisconceptionElapsed time can be found by subtracting the times like ordinary whole numbers straight down the columns, for example 4:10 minus 2:45 becomes '2 hours 65 minutes' or a negative minute count.
Why it happens: Column subtraction is the most recently drilled subtraction method, but a clock regroups in 60s, not 10s, so borrowing 1 hour must add 60 minutes, not 10, and students have not yet been told that explicitly for this context.
How to address it: Teach counting on in jumps (to the next o'clock, then whole hours, then leftover minutes) as the default method for elapsed time and avoid column subtraction of clock times altogether at this grade.
MisconceptionConverting kilograms to grams means dividing by 1000, since 'converting' often means making a smaller-looking number.
Why it happens: Students over-generalise from other conversions or simply guess the operation direction rather than reasoning about which unit is smaller.
How to address it: Ask first: will there be more grams or fewer grams than kilograms? Grams are smaller, so there will be more of them, which means multiply. Anchor with 'kilo means 1000'.
MisconceptionA bigger-looking or bulkier object always has a greater mass than a smaller one, for example a large inflated balloon versus a small metal key.
Why it happens: Size is the most visible feature, so students substitute it for mass rather than thinking about density and material.
How to address it: Hold both objects, or place them on a balance scale, and let the scale be the judge. Size and mass are different properties.
Guided practice (with answers)
1. The hour hand is between 7 and 8, and the minute hand is 2 marks past the 9. What time is it?
Answer: 7:47. The 9 is 45 minutes (5x9), plus 2 more marks is 47 minutes, and the hour is still 7.
2. A school day starts at 8:50am and ends at 3:15pm. Roughly how many hours and minutes is that? (jump to 9:00, then hours, then leftover minutes)
Answer: 6 hours 25 minutes: 8:50 to 9:00 is 10 min, 9:00 to 3:00 is 6 hours, 3:00 to 3:15 is 15 min; 10 + 15 = 25 min plus 6 hours.
3. Convert 4 kg 250 g to grams.
Answer: 4250 g, since 4 kg = 4000 g and 4000 + 250 = 4250.
4. Convert 3600 mL to litres and millilitres.
Answer: 3 L 600 mL, since 3600 ÷ 1000 = 3 remainder 600.
5. A bottle holds 2 L. After pouring out 650 mL, how much is left?
Answer: 1350 mL (1 L 350 mL), since 2000 - 650 = 1350.
Independent practice worksheets
Set the matching ChalkBee worksheets for independent work. The answer keys are computed in code, so they are never wrong. Split practice across a lesson each for time, mass, and volume.
Differentiation
- For telling time, cover the hour hand and practise reading only the minute hand's five-then-one count before combining both hands.
- For elapsed time, always draw the jump line, even for a mentally easy example, to build the habit before removing the scaffold.
- For mass and volume, keep a laminated 1 kg = 1000 g and 1 L = 1000 mL reference card on the desk.
- Elapsed time problems that cross noon or midnight (am to pm).
- Two-step mass or volume problems, such as combining three containers then finding how much more is needed to reach a target.
- Ask students to write their own elapsed-time word problem using their actual daily schedule.
Assessment: exit ticket
A short exit ticket sampling all three skills: reading the clock, elapsed time, and a mass or volume conversion.
1. The hour hand is between 5 and 6, the minute hand is on the 2. What time is it?
Answer: 5:10, since the 2 mark is 5x2=10 minutes.
2. A train leaves at 10:40am and arrives at 12:05pm. How long is the trip?
Answer: 1 hour 25 minutes: 10:40 to 11:00 is 20 min, 11:00 to 12:00 is 60 min, 12:00 to 12:05 is 5 min; 20+60+5=85 min = 1 h 25 min.
3. Convert 2 L 80 mL to millilitres.
Answer: 2080 mL, since 2 L = 2000 mL and 2000 + 80 = 2080.
Teacher notes and timings
- Rough timing across three lessons: Lesson 1 telling time to the minute (section 1), Lesson 2 elapsed time (section 2), Lesson 3 mass and volume plus the exit ticket (section 3 and assessment).
- The jump-line method for elapsed time in section 2 is the same 'count on in friendly amounts' strategy used for money change; if your class has taught making change, name that connection explicitly.
- Language to keep saying: short and slow for hours, long and fast for minutes; more of the smaller unit means multiply, fewer of the bigger unit means divide.
- Curriculum note: ACARA's Year 3 descriptor AC9M3M03 covers time and am/pm at the same year as the US Grade 3 standard, and AC9M3M01 folds mass and volume into a broader 'read scaled instruments' descriptor rather than a dedicated mass-and-volume standard, so this unit maps cleanly onto both.
- Present mode and print both work: use Present to model the jump-line method live, then print the worksheets for independent practice.