Does an Hour Have 100 Minutes?

Why do people think an hour has 100 minutes?

Payroll systems, timesheets and calculators often display working time using numbers such as 7.50, 8.25 and 6.75.

If you are used to normal clock time, it is easy to assume the digits after the decimal point are minutes. They are not. They represent a fraction of one hour.

For example, 7.50 hours means 7 hours + 0.50 of an hour. Because half an hour is 30 minutes:

7.50 hours = 7h30m

60 minutes vs 100 hundredths

A normal hour contains 60 minutes. A decimal hour can be divided into 100 hundredths.

Those are two different ways of describing the same hour.

One hundredth of an hour is 0.01 hour. Convert that into minutes:

0.01 × 60 = 0.6 minutes = 36 seconds

So there are 100 hundredths in 1.00 hour, but there are still only 60 standard minutes in an hour.

This is the key difference.

Why is 30 minutes 0.50 hours?

Thirty minutes is half of a normal 60-minute hour. The calculation is:

30 ÷ 60 = 0.50

So 30 minutes = 0.50 hours.

It is not 0.30 hours, because 0.30 of an hour is:

0.30 × 60 = 18 minutes

Therefore 0.30 hours = 18 minutes.

This is one of the easiest ways to see why decimal hours cannot be read like normal clock minutes.

Quick decimal-time comparison

Notice that 30 minutes = 0.50, not 0.30. And 45 minutes = 0.75, not 0.45.

7:30 is not the same as 7.30

This is one of the most common decimal-time mistakes.

Normal clock time 7:30 means 7 hours 30 minutes. Convert the 30 minutes:

30 ÷ 60 = 0.50

So 7h30m = 7.50 decimal hours.

But 7.30 decimal hours means 7 hours + 0.30 hour. Convert 0.30 hour:

0.30 × 60 = 18 minutes

So 7.30 decimal hours = 7h18m, and 7:30 is not 7.30.

The colon normally separates hours and minutes. The decimal point represents a fraction of an hour.

For the full explanation, see Why 7.30 Hours Is Not 7 Hours 30 Minutes.

What does “100-minute clock” actually mean?

The phrase 100-minute clock is often used informally when talking about decimal hours, particularly around payroll and timesheets.

The wording can be misleading. It may sound as though the normal hour has been changed from 60 minutes to 100 minutes. That is not what usually happens.

Instead, 1 hour = 1.00 decimal hours, and that 1.00 can be divided into 100 hundredths. The underlying hour still contains 60 standard minutes.

For a fuller explanation of the phrase itself, see What Is a 100-Minute Clock?

Does payroll use 100-minute hours?

No. Payroll systems that use decimal hours still start with normal 60-minute hours.

For example, suppose you work 8h45m. Convert the minutes:

45 ÷ 60 = 0.75

So 8h45m = 8.75 decimal hours, not 8.45.

The decimal format simply makes calculations such as pay easier.

For more detail, see Decimal Hours for Payroll Explained.

Why use decimal hours?

Decimal hours make time easier to use in calculations.

For example, worked time of 7h30m is 7.50 hours. At an hourly rate of £15:

7.50 × £15 = £112.50

That is simpler for payroll, billing and timesheet systems than trying to multiply an hourly rate directly by mixed hours and minutes.

What would a true 100-minute hour mean?

It is possible to design a different time system where an hour is divided into 100 specially defined units.

But those units would not be the same as the ordinary minutes used on a normal clock.

In everyday timekeeping, 1 hour = 60 minutes.

When Hundred Hour talks about decimal hours, it is describing the normal 60-minute hour expressed as a decimal.

Common mistakes

Thinking 1.00 means 100 minutes

It does not. 1.00 hour = 60 minutes.

Thinking 0.50 means 50 minutes

It means 30 minutes.

Thinking 0.30 means 30 minutes

It means 18 minutes.

Treating the digits after the decimal as minutes

Decimal hours represent fractions of an hour. They are not HH:MM notation.

Assuming a “100-minute clock” literally has 100 standard minutes

The phrase usually refers to decimal time or hundredths of an hour.

Confusing 7:30 with 7.30

7:30 = 7h30m = 7.50 decimal hours, while 7.30 decimal hours = 7h18m.