Time, Units of Time and Timetables

Q: Which mathematical operation do you use to convert a larger unit of time into a smaller unit?

Use multiplication to convert from a larger unit of time to a smaller unit.

Q: Which mathematical operation do you use to convert a smaller unit of time into a larger unit?

Use division , where the quotient gives the larger unit and any remainder gives the leftover smaller units.

Q: Why is it incorrect to treat time calculations like regular base-\(100\) decimals?

Time is not based on \(100\); \(1\text{ hour}\) has \(60\) minutes and \(1\text{ minute}\) has \(60\) seconds , not \(100\).

Q: What must you do before comparing two different time durations?

Always convert both durations into the same unit before comparing them.

Mathematics · Primary School (Thailand) · 6 min read · Updated: 22 Oct 2026

Welcome to the Fun World of "Time" and "Timetables"!

Have you ever wondered why a day seems to fly by so fast? Or have you ever had to check a bus schedule, a class timetable, or a TV guide? Time is all around us every single day! Learning about units of time, how to convert between them, and how to read timetables will help you plan your daily life brilliantly and make the most of your time.

If it feels a bit tricky at first, don't worry at all... Let's take it step by step with easy-to-understand examples, and you will see that learning about time is fun and much easier than you think!

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1. Units of Time and Their Relationships

We use different units to measure time, from tiny units that tick away in a flash to large units that span many days or years. Let's get to know these units and remember how they are related!

The Time Family: From Smallest to Largest Units

• \(60\) seconds equal \(1\) minute (try blinking or counting from \(1\) to \(60\) slowly—that is about \(1\) minute!)
• \(60\) minutes equal \(1\) hour (about the length of \(1\) class period)
• \(24\) hours equal \(1\) day (the time it takes Earth to complete \(1\) full spin on its axis, giving us day and night)
• \(7\) days equal \(1\) week (Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday)
• \(30\) days or \(31\) days equal \(1\) month (months ending in "-ber", April, and June have \(30\) days, while January, March, May, July, August, October, and December have \(31\) days, except February which has \(28\) or \(29\) days)
• \(12\) months equal \(1\) year
• \(365\) days or \(366\) days equal \(1\) year (or about \(52\) weeks)

Did You Know?

February usually has \(28\) days, but every \(4\) years it gets an extra day and has \(29\) days, making that year have \(366\) days in total. We call a year with \(366\) days a "leap year"!

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2. Converting Units of Time (Mastering Time Conversions)

There are \(2\) golden rules to keep in mind when converting units of time:

1. To convert from a "larger unit" to a "smaller unit", use "multiplication".
Example: Convert hours to minutes.
Since \(1\) hour = \(60\) minutes,
then \(3\) hours = \(3 \times 60 = 180\) minutes.

2. To convert from a "smaller unit" to a "larger unit", use "division".
Example: Convert minutes to hours.
If we have \(140\) minutes, how many hours and minutes is that?
Divide \(140\) by \(60\):
\(140 \div 60 = 2\) with a remainder of \(20\)
The quotient gives the number of hours, and the remainder gives the remaining minutes.
Therefore, \(140\) minutes is equal to \(2\) hours and \(20\) minutes.

Another Example: Weeks and Days

Ploy went to camp for \(25\) days. How many weeks and days is that?
• We know that \(7\) days = \(1\) week (converting from a smaller unit to a larger unit, so we divide).
• Calculation: \(25 \div 7 = 3\) with a remainder of \(4\)
• Answer: Ploy stayed at camp for \(3\) weeks and \(4\) days.

Common Mistake to Avoid

Many students accidentally treat time like base-\(100\) decimals, thinking that \(1\) hour equals \(100\) minutes. That is incorrect! Always remember: \(1\) hour = \(60\) minutes and \(1\) minute = \(60\) seconds!

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3. Finding and Comparing Time Intervals (Elapsed Time)

Elapsed time is the duration that passes from the start of an activity to the end of it.

An Easy Way to Find Elapsed Time (Jumping Along the Number Line)

Suppose Kla starts his homework at \(16:40\) and finishes at \(18:15\). How long did Kla spend doing his homework?

We can break it down into easy jumps:
• Step 1: Jump from \(16:40\) forward to the next full hour, which is \(17:00\). That takes \(20\) minutes.
• Step 2: Jump from \(17:00\) forward to \(18:00\). That takes \(1\) hour.
• Step 3: Jump from \(18:00\) to the finish time at \(18:15\). That takes \(15\) minutes.
• Add up all the jumps: \(1\) hour and \(20 + 15 = 35\) minutes.
Therefore, Kla spent \(1\) hour and \(35\) minutes on his homework.

Comparing Time Durations

Whenever you want to compare which duration is longer or shorter, always convert them to the same unit first!

Example: Who spent more time reading: Fahsai, who read for \(100\) minutes, or Tawan, who read for \(1\) hour and \(45\) minutes?
• Convert Tawan's time to minutes: \(1\) hour (\(60\) minutes) \(+ 45\) minutes \(= 105\) minutes.
• Compare: Fahsai (\(100\) minutes) is less than Tawan (\(105\) minutes).
• Conclusion: Tawan spent more time reading than Fahsai.

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4. Reading Timetables

A timetable is a schedule that shows the times at which planned events or activities will take place. You will see them in school schedules, train or bus timetables, and field trip itineraries.

Example: Grade 4 Field Trip Schedule

\(08:00\) : Gather and board the bus at school
\(08:30\) : The bus departs for the zoo
\(09:45\) : Arrive at the zoo and visit the wildlife exhibit
\(12:00\) : Lunch break
\(13:00\) : Watch the dolphin show
\(14:30\) : Board the bus to head back to school
\(15:45\) : Arrive safely back at school

Let's Practice Answering Questions from the Timetable:

Question 1: How long did the bus journey from the school to the zoo take?
How to think: The bus departed at \(08:30\) and arrived at \(09:45\).
• From \(08:30\) to \(09:30\) is \(1\) hour.
• From \(09:30\) to \(09:45\) is \(15\) minutes.
Answer: The journey took \(1\) hour and \(15\) minutes.

Question 2: How long was the students' lunch break?
How to think: Lunch started at \(12:00\) and the next activity began at \(13:00\).
• From \(12:00\) to \(13:00\) is exactly \(1\) hour.
Answer: The lunch break was \(1\) hour long (or \(60\) minutes).

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5. Word Problems Involving Time

Here is a handy \(4\)-step secret to solving time word problems easily: 1. Read and understand the problem \(\rightarrow\) 2. Plan whether to add or subtract \(\rightarrow\) 3. Show your working \(\rightarrow\) 4. Check if your answer makes sense.

Example Problem: Dad's Road Trip

Problem: Dad drove upcountry. The trip there took \(3\) hours and \(45\) minutes. On the return trip, heavy traffic made the drive take \(50\) minutes longer than the trip there. How long did Dad's return trip take?

Analysis:
• The outward journey took: \(3\) hours and \(45\) minutes.
• The return journey took "\(50\) minutes longer" (so we need to add the times).

Working:
• Add the minutes first: \(45\) minutes \(+ 50\) minutes \(= 95\) minutes.
• Since \(95\) minutes is more than \(60\) minutes, convert it into hours and minutes:
\(95 \div 60 = 1\) hour and \(35\) minutes.
• Regroup (carry over) the \(1\) hour with the existing hours: \(3\) hours \(+ 1\) hour \(= 4\) hours.
• That leaves \(35\) minutes.

Answer: Dad's return trip took \(4\) hours and \(35\) minutes.

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Key Takeaways to Remember

• Quick Reference Facts:
- \(1\) minute = \(60\) seconds
- \(1\) hour = \(60\) minutes
- \(1\) day = \(24\) hours
- \(1\) week = \(7\) days
- \(1\) year = \(12\) months (or \(365\) / \(366\) days)
• Conversions: Large to small, multiply; small to large, divide.
• Elapsed Time: Look at the start time and end time, then jump forward to the nearest full hour step by step—this helps prevent calculation errors!
• Reading Timetables: Pay attention to the column headers and align the times with the matching activities to find the exact details you need.

Awesome job, everyone! Keep practicing with different problems, and working with time will become second nature to you!

Quick check

Can you answer these now?

Open each question to check the key ideas from this chapter.

What are the relationships between seconds, minutes, hours, days, weeks, months, and years?

\(1\text{ min} = 60\text{ s}\), \(1\text{ h} = 60\text{ min}\), \(1\text{ day} = 24\text{ h}\), \(1\text{ week} = 7\text{ days}\), \(1\text{ year} = 12\text{ months}\), and \(1\text{ year} = 365\) or \(366\text{ days}\).

What is a leap year, and how many days does it have?

A leap year occurs every \(4\) years when February has \(29\) days instead of \(28\), giving the year a total of \(366\) days.

Which mathematical operation do you use to convert a larger unit of time into a smaller unit?

Use multiplication to convert from a larger unit of time to a smaller unit.

Which mathematical operation do you use to convert a smaller unit of time into a larger unit?

Use division, where the quotient gives the larger unit and any remainder gives the leftover smaller units.

Why is it incorrect to treat time calculations like regular base-\(100\) decimals?

Time is not based on \(100\); \(1\text{ hour}\) has \(60\) minutes and \(1\text{ minute}\) has \(60\) seconds, not \(100\).

How can you find elapsed time using the number line jumping method?

Jump forward from the start time to the next whole hour, jump across full hours, jump to the end time, and then add all the jumps together.

What must you do before comparing two different time durations?

Always convert both durations into the same unit before comparing them.

What is a timetable and how do you find the duration of an activity from it?

A timetable is an organized schedule of events; find an activity's duration by calculating the elapsed time between its start time and the start time of the next event.

What are the four steps to solving time word problems?

The four steps are: 1. Read and understand, 2. Plan (add or subtract), 3. Show your working, and 4. Check your answer.

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