Units of Time for Kids: Seconds, Minutes, Hours, Days

What Are The Units Of Time?

The units of time, from smallest to largest in everyday use, are the second, minute, hour, day, week, month, year, decade, century and millennium. Each is a fixed unit except the month, which changes length.

A child does not need all eleven at once. Seconds, minutes, hours, days and weeks come first; months, years and the leap year come next; decades and centuries arrive with history lessons.

Why Are There 60 Minutes In An Hour Instead Of 100?

There are 60 minutes in an hour because the Babylonians did their astronomy in base 60, a system they inherited from the Sumerians, who developed it around 2000 BC. Later Greek astronomers used base 60 to split degrees into minutes and seconds, and timekeeping followed.

Nobody knows exactly why 60 was chosen. It is convenient, though: as NIST's Michael Lombardi explains, 60 "is the smallest number divisible by the first six counting numbers as well as by 10, 12, 15, 20 and 30" (Scientific American, 2007). That is why half an hour, a third of an hour and a quarter of an hour are all whole numbers of minutes (30, 20 and 15).

The 24-hour day comes from a different place. The Egyptians split daylight into 12 parts and night into 12 parts, and once both were divided, "the concept of a 24-hour day was in place," as Lombardi puts it. So the day is built on 12s and the hour on 60s, and neither is built on 10. That single fact explains most of the mistakes later in this guide.

How Do You Convert Between Units Of Time?

Convert units of time by multiplying when you go to a smaller unit and dividing when you go to a bigger unit. The number you multiply or divide by is the size of the step: 60 between seconds, minutes and hours; 24 between hours and days; 7 between days and weeks.

$$3,\text{h} = 3 \times 60,\text{min} = 180,\text{min}$$

$$420,\text{s} = 420 \div 60,\text{min} = 7,\text{min}$$

A quick check before any calculation saves most errors: "Will there be more of the smaller unit, or fewer?" There are always more minutes than hours in the same stretch of time, so the minutes number must be bigger. Fast recall of the 6 and 12 rows of the multiplication table makes these conversions much smoother.

How Do You Convert Minutes To Hours?

Divide the minutes by 60. The whole-number part is the hours and the remainder is the leftover minutes.

$$135 \div 60 = 2 \text{ remainder } 15$$

So 135 minutes is 2 hours 15 minutes. Mixed answers like "2 h 15 min" are what children use in grades 3 and 4.

How Do You Convert Minutes To Decimals Of An Hour?

Divide the leftover minutes by 60 to get a decimal. Fifteen minutes is $\frac{15}{60} = 0.25$ of an hour, so 2 hours 15 minutes is 2.25 hours, not 2.15 hours. The link between fractions, decimals and percentages is what makes this click, and it usually arrives around grades 5 and 6.

How Many Weeks Are In A Month?

A month has 4 full weeks plus 0 to 3 extra days. February has exactly 4 weeks (28 days) except in a leap year, a 30-day month has 4 weeks and 2 days, and a 31-day month has 4 weeks and 3 days. On average, a month is about 4.35 weeks.

The knuckle trick is the classic way to remember month lengths. Make two fists side by side and count across the knuckles and the dips between them: every knuckle is a 31-day month, every dip a shorter month.

Why Is A Year Not Exactly 365 Days?

A year is not exactly 365 days because the Earth takes about 365 and a quarter days to go around the Sun. The calendar adds a leap day, 29 February, to keep up.

The rule has three parts, and the third surprises most adults:

• Every year divisible by 4 is a leap year (2024, 2028).

• Except century years, which are not leap years (1900, 2100).

• Unless the century year is divisible by 400, which makes it a leap year again (2000).

The result is an average calendar year of 365.2425 days (Wikipedia, Unit of time). Even the second gets adjusted now and then: international timekeepers agreed in 2022 to change how leap seconds are handled, in or before 2035 (BIPM, CGPM 2022 Resolution 4).

How Do You Calculate Elapsed Time?

Calculate elapsed time by counting up from the start time to the end time in friendly jumps: first to the next whole hour, then whole hours, then the leftover minutes. Elapsed time means "how much time passed," such as the length of a swim lesson or a car trip.

A number line makes the jumps visible:

1. Write the start time on the left and the end time on the right.

2. Jump from the start to the next o'clock.

3. Jump in whole hours as far as you can.

4. Jump the remaining minutes.

5. Add the jumps.

This is counting on, the same strategy children use in mental math, just with 60 minutes in each hour instead of 10 ones in each ten. The Common Core grade 3 standard asks children to solve these problems "by representing the problem on a number line diagram" (Common Core 3.MD.A.1).

How Do You Calculate Elapsed Time From PM To AM?

Split the time at midnight. Count from the p.m. start to 12:00 midnight, then from midnight to the a.m. end, and add the two parts. Example 6 below walks through a bedtime-to-wake-up problem this way.

Examples Of Units Of Time

Example 1

How many seconds are in 5 minutes?

Minutes are bigger than seconds, so multiply by 60.

$$5 \times 60 = 300$$

There are 300 seconds in 5 minutes.

Example 2

A swim lesson starts at 9:45 and ends at 10:15. How long is the lesson?

A tempting shortcut treats the times like ordinary numbers:

$$1015 - 945 = 70$$

That gives 70 minutes, which is longer than an hour, yet 9:45 to 10:45 would already be a full hour. Something broke. The subtraction assumed 100 minutes in an hour, because 945 and 1015 are base-10 numbers.

Count up instead. From 9:45 to 10:00 is 15 minutes; from 10:00 to 10:15 is another 15 minutes.

$$15 + 15 = 30$$

The lesson is 30 minutes long.

Example 3

Write 135 minutes in hours and minutes, and then as a decimal number of hours.

Divide by 60.

$$135 \div 60 = 2 \text{ remainder } 15$$

That is 2 hours 15 minutes. For the decimal, change the 15 minutes into hours.

$$\frac{15}{60} = 0.25$$

So 135 minutes is 2.25 hours.

Example 4

How many hours are in one week?

A week is 7 days and each day is 24 hours.

$$7 \times 24 = 168$$

There are 168 hours in a week.

Example 5

A movie starts at 7:40 p.m. and lasts 1 hour 55 minutes. What time does it end?

Add the whole hour first.

$$7{:}40 + 1,\text{h} = 8{:}40$$

Then split the 55 minutes into 20 (to reach 9:00) and 35.

$$8{:}40 + 20,\text{min} = 9{:}00$$

$$9{:}00 + 35,\text{min} = 9{:}35$$

The movie ends at 9:35 p.m. Check: $20 + 35 = 55$.

Example 6

A child falls asleep at 8:30 p.m. and wakes at 6:45 a.m. How long did the child sleep?

Split at midnight.

From 8:30 p.m. to 12:00 midnight is 3 hours 30 minutes. From 12:00 midnight to 6:45 a.m. is 6 hours 45 minutes. Add the parts.

$$3,\text{h}\ 30,\text{min} + 6,\text{h}\ 45,\text{min} = 9,\text{h}\ 75,\text{min}$$

Seventy-five minutes is more than an hour, so regroup 60 of them.

$$9,\text{h}\ 75,\text{min} = 10,\text{h}\ 15,\text{min}$$

Check: 8:30 p.m. to 6:30 a.m. is 10 hours, and 6:30 to 6:45 adds 15 minutes.

What Age Do Kids Learn Time?

Kids learn units of time in steps between about age 5 and 10: hours and half hours first, then five-minute times and a.m./p.m., then minutes and elapsed time, then converting between units. England's National Curriculum covers each step about a year earlier than the US Common Core.

The US grade 2 standard reads "tell and write time from analog and digital clocks to the nearest five minutes, using a.m. and p.m." (Common Core 2.MD.C.7). England's Year 3 programme asks children to "know the number of seconds in a minute and the number of days in each month, year and leap year," and Year 5 to "solve problems involving converting between units of time" (National Curriculum in England, mathematics, GOV.UK). Speed, distance and the time formula come later, usually in middle school.

What Units Of Time Activities Work At Each Age?

Time activities work best when your child feels the length of a unit before converting it. Choose from the band that fits your child.

Ages 4 to 6

• One-Minute Challenge: Set a timer for one minute and count how many jumps, claps or blocks stacked fit inside it.

• Days Of The Week Chart: Put a sticker on today's day each morning and say yesterday, today and tomorrow out loud.

• Before And After: Lay out picture cards of the morning routine and put them in order.

Ages 6 to 8

• Thirty-Second Guess: Your child says "stop" when they think 30 seconds have passed, and you check the timer.

• Birthday Countdown: Count the days left until a birthday on a paper calendar, then rewrite it in weeks and days.

• Our 24 Hours: Shade a 24-square strip for sleep, school, meals and play, and check the parts add to 24.

Ages 8 to 10

• TV Guide Elapsed Time: Pick two programmes and find how long each lasts using a number line.

• Conversion Race: Who can work out first how many seconds are in an hour (3,600)?

• Leap Year Detective: Decide whether 1900, 2000, 2024 and 2100 are leap years using the three-part rule.

Ages 10 and up

• Age In Seconds: Estimate a 10-year-old's age in seconds ($10 \times 365.25 \times 86{,}400 = 315{,}576{,}000$, about 315 million).

• 24-Hour Timetable: Read a train timetable in 24-hour time and find journey lengths.

• Clock Face Numerals: Find a clock with Roman numerals and read times from it.

What Signs Show Your Child Needs More Practice With Time?

The clearest sign is an elapsed-time answer bigger than 60 minutes for a stretch shorter than an hour. It means your child is still subtracting clock times as base-10 numbers.

Other signs to watch for:

• Decimal mix-ups. "Two and a half hours" is written as 2 hours 50 minutes.

• Lost at midnight or noon. Elapsed time that crosses 12:00 comes out wrong or negative.

• Month guesses. Your child assumes every month is 30 days, or every month is exactly 4 weeks.

• Backwards conversions. Hours to minutes gives a smaller number than they started with.

The rusher tends to show the first sign: they see two times, subtract, and move on. Asking "is that more or less than an hour?" before writing anything is usually enough to slow them down.

Where Do Kids Go Wrong With Units Of Time?

Most time mistakes come from one source: treating time as if it counts in tens.

Mistake 1: Subtracting Clock Times Like Ordinary Numbers

Where it slips in: Elapsed time problems such as 9:45 to 10:15.

Don't do this: Don't write $1015 - 945 = 70$.

The correct way: Count up to the next o'clock, then count on, as in Example 2.

The first instinct of most children who have just learned column subtraction is to use it here, and it works for 9:15 to 9:45 (30 minutes), which makes the habit stick. The fix is a number line with the o'clock marked as a stopping point.

Mistake 2: Reading Decimal Hours As Minutes

Where it slips in: Phrases like "2.5 hours" in recipes, travel times and word problems.

Don't do this: Don't read 2.5 hours as 2 hours 50 minutes.

The correct way: Half of 60 is 30, so 2.5 hours is 2 hours 30 minutes. A quarter hour (0.25) is 15 minutes.

The memorizer often knows "0.5 means half" in money and length but has never been asked what half an hour is in minutes. One conversation about $\frac{1}{2}$ of 60 usually clears it.

Mistake 3: Forgetting The Midnight Or Noon Switch

Where it slips in: Elapsed time from p.m. to a.m., or from morning to afternoon.

Don't do this: Don't subtract 6:45 from 8:30 and call it the sleep time.

The correct way: Split the problem at 12:00, as in Example 6.

Mistake 4: Assuming Every Month Is The Same Length

Where it slips in: Counting days to an event, or converting months to weeks.

Don't do this: Don't treat every month as 30 days or exactly 4 weeks.

The correct way: Use the knuckle trick or a calendar, and remember a month is 4 weeks plus 0 to 3 days.

Mistake 5: Converting In The Wrong Direction

Where it slips in: Hours to minutes, minutes to seconds.

Don't do this: Don't divide 3 hours by 60.

The correct way: Ask "more or fewer?" first. More minutes than hours, so multiply: $3 \times 60 = 180$.

When Should You Get Outside Help With Time?

Time is one of the slower skills to settle, and occasional mix-ups are normal through grade 3. A conversation with your child's teacher makes sense when:

• By the end of grade 3 (Year 4 in England), your child still cannot say how many minutes are in an hour or hours are in a day without counting.

• Elapsed time within one hour (such as 3:20 to 3:55) is still out of reach after several weeks of number-line practice.

• Your child cannot yet name the days of the week in order by around age 7.

• Time questions regularly end in frustration or refusal.

None of these is a diagnosis. Time skills rest on counting on and on knowing the 60s, so the teacher's view of those skills is the useful next step.

How Does Bhanzu Teach Units Of Time?

Bhanzu teaches units of time by starting with why: why an hour has 60 minutes, why the calendar needs leap years, why clock times cannot be subtracted like ordinary numbers. Children who know the reason make far fewer of the base-10 mistakes above.

Classes are live and online for students from UKG (around age 5) to Grade 10. Each child starts from their actual level rather than their school grade, so a nine-year-old who never secured five-minute times gets that first, before elapsed time and conversions.

Bhanzu fits families who want a trained teacher to build reasoning-first understanding of time, conversions and word problems alongside practice at home. It is not the right fit if you only want clock-reading worksheets or quick test preparation, or for a child under about five, who is better served by daily routines and calendar talk at home.

Where Can Your Child Get Extra Help With Units Of Time?

If you would like structured support with time, conversions and elapsed time, these pages match the grades where time is taught:

• 1st grade math tutor for hours, half hours and days of the week.

• 2nd grade math tutor for five-minute times and a.m. and p.m.

• 3rd grade math tutor for elapsed time and minutes.

• Elementary math tutor for converting units and time word problems.

Wrapping Up

• The units of time climb in steps of 60, 60, 24 and 7, not in tens, which is the root of most time mistakes.

• An hour has 60 minutes because of Babylonian base-60 astronomy, and 60 splits neatly into halves, thirds and quarters.

• Multiply to convert to a smaller unit; divide to convert to a bigger unit; check "more or fewer?" first.

• Find elapsed time by counting up to the next o'clock on a number line, and split at midnight or noon.

• A month is 4 weeks plus 0 to 3 days, and a year is 365 days with a leap day most fourth years.

What Should You Practise This Week?

Pick one routine each day and time it with your child: brushing teeth, the walk to school, dinner. Write each start and end time, find the elapsed time on a number line, and once a week convert the longest one into seconds.

If elapsed time keeps coming out over 60, go back to Example 2 and practise only the jump to the next o'clock for a few days. Turning these into short math word problems is a good next step. For a live teacher who builds time and conversion skills the same reasoning-first way, book a free demo class with Bhanzu.

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