How to convert from 24 hour to 12 hour time

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Spirometry, the measurement of volumes of air moving into and out of the respiratory system, helps doctors detect and treat respiratory diseases. A spirometer contains a mouthpiece attached to a volume indicator or airflow transducer; advanced models produce a graphical spirogram. You can calculate respiratory volumes, capacities (the sum of two or more volumes) and rates using a spirogram or spirometer lab data 2. Fluctuations in these calculations usually imply respiratory disease.

Calculate tidal volume (TV), an indicator of air volume during normal breathing, on a nonrecording (dry) spirometer by finding the mean volume of three normal exhalations. On a spirogram, measure the distance between the crests and troughs of the small waves, then find the mean of these values 2. In a classroom setting, ask your lab instructor whether you need to correct for differences in body temperature, pressure and saturation (BTPS) and the conditions in the lab environment and, if so, which correction factor to use.

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Compute expiratory reserve volume (ERV), the maximum volume of air exhaled beyond the exhalation of a normal breath, on a dry spirometer by having the test subject exhale maximally into the mouthpiece after exhaling normally. On a spirogram, find the difference between the trough of the lowest wave and the trough of the closest tidal volume wave and correct for BTPS.

Calculate vital capacity (VC), the maximum possible volume of air exhaled and inhaled, on a dry spirometer by having the subject inhale the maximum amount of air, then exhale as forcibly as possible into the mouthpiece. On a spirogram, calculate VC by finding the sum of inspiratory reserve volume (see step 5) plus tidal volume plus expiratory reserve volume (VC = TV + IRV + ERV).

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Multiply vital capacity by the factor for your subject’s age group to obtain residual volume (RV), or the volume of air remaining in the lungs after maximal exhalation (RV = VC x factor).

Obtain inspiratory reserve volume (IRV), the maximum possible amount of air inhaled beyond the inhalation of a normal breath, on a dry spirometer by finding the sum of the tidal volume and expiratory reserve volume and subtracting this value from the vital capacity (IRV = VC – (TV + ERV)). On a spirogram, measure the distance between the crest of the tallest wave and the crest of the preceding tidal volume wave and correct for BTPS, then calculate vital capacity (go back to step 3).

Find the sum of the tidal volume plus inspiratory reserve volume to obtain inspiratory capacity (IC), the maximum possible amount of air inspired above a normal exhalation. On a spirogram, subtract the value for the expiratory trough immediately before the maximal inspiratory peak from the inspiratory peak value and correct for BTPS (IC = TV + IRV).

Add the expiratory reserve volume plus the residual volume to get functional residual capacity (FRC), a measure of how much air remains in the lungs after a normal exhalation (FRC = ERV + RV).

Find the total lung capacity (TLC), or the total volume of air that the respiratory system holds, by adding the inspiratory and expiratory reserve volumes plus tidal volume and residual volume (TLC = IRV + ERV + TV + RV).

Measure the amount of air expired during the first second of the forced expiratory vital capacity test, when the test subject inspired and expired maximally as rapidly as possible. This gives you forced expiratory vital capacity (FVC), which indicates pulmonary health.

Multiply the tidal volume times the respiratory rate, or the number of breaths taken per minute, to get minute respiratory volume (MRV). This represents the total amount of air moved into and out of the respiratory system each minute (MRV = TV x respiratory rate).

Female volumes and capacities average 20 percent to 25 percent less than those of adult males. Age, body size, physical conditioning and certain diseases, disorders and injuries also affect respiratory volumes and capacities.


Do not attempt to diagnose any disease from these calculations. If you suspect a respiratory disease or disorder, consult a doctor immediately.

In this tutorial, we are going to learn how to Convert 24 hour format to 12 hour format in C++.

This program converts 24 to 12 hour format.

How to Input the clock format in C++

The time should be in HH:MM:SS where HH denotes Hours, MM denotes Minutes and SS is Seconds.

How to use AM/PM notation?

  • We denote 00:00 as 00:00 AM
  • 12:00 as 12:00 PM
  • 23:00 as 23:00 PM

In this 24 to 12 hour conversion, the hour value is changed and not the minute value.

In the above code, the input variable is twenty_four_hrs. Then the variables hrs and min are declared as integer as time belongs to integer datatype.

How to separate hours and minutes?

On dividing the input time by 100, we will get the hours which is stored in the variable name called hrs.

The same way the minutes on doing, twenty_four_hrs%100, we can get the minutes which is stored into the variable name called min.


In the above code,

  • if condition checks, hrs is equal to 00 and hrs not equal to 12 (i.e)00 is nothing but 12 .
  • else if condition checks whether hrs is equal to 12 and hrs not equal to 0 then hrs remains with the same 12 denoted in PM.
  • else if hrs less than 12 and hrs not equal to 0 then both the hrs and min remains the same.
  • if hrs greater 12 and hrs not equal to 0 then hrs=hrs-12 , min remains the same.


C++ program to convert 24 hour format to 12 hour format

When the input is 1245 the hrs=1245/100 becomes 12 and min=0045%100 becomes 45 and from the given conditions.

Then hrs is compared on checking it enters the second else if statement where the hrs and minute remains the same and the output is,

Thus the program coverts from 24 to 12 hour format.


We hope this tutorial helped you to understand how to convert 24 hour format to 12 hour format in C++.

I have TimeSpan data represented as 24-hour format, such as 14:00:00, I wanna convert it to 12-hour format, 2:00 PM, I googled and found something related in stackoverflow and msdn, but didn’t solve this problem, can anyone help me? Thanks in advance.

Update Seems that it’s possible to convert 24-hour format TimeSpan to String, but impossible to convert the string to 12-hour format TimeSpan 🙁

But I still got SO MANY good answers, thanks!

8 Answers 8

TimeSpan represents a time interval not a time of day. The DateTime structure is more likely what you’re looking for.

How to convert from 24 hour to 12 hour time

(Summing up my scattered comments in a single answer.)

First you need to understand that TimeSpan represents a time interval. This time interval is internally represented as a count of ticks an not the string 14:00:00 nor the string 2:00 PM . Only when you convert the TimeSpan to a string does it make sense to talk about the two different string representations. Switching from one representation to another does not alter or convert the tick count stored in the TimeSpan .

Writing time as 2:00 PM instead of 14:00:00 is about date/time formatting and culture. This is all handled by the DateTime class.

However, even though TimeSpan represents a time interval it is quite suitable for representing the time of day ( DateTime.TimeOfDay returns a TimeSpan ). So it is not unreasonable to use it for that purpose.

To perform the formatting described you need to either rely on the formatting logic of DateTime or simply create your own formatting code.

The format specifiers using in ToString are documented on the Custom Date and Time Format Strings page on MSDN. It is important to specify a CultureInfo that uses the desired AM/PM designator. Otherwise the tt format specifier may be replaced by the empty string.

Using custom formatting:

Admittedly this solution is quite a bit more complex than the first method.

If you don’t like the 24-hour time format in Windows 10, follow these simple steps to change the 24-hour clock to a 12-hour clock.

On Windows 10, the clock generally appears at the bottom right corner of the taskbar. Like with any operating system, Windows 10 lets you choose between 24-hour and 12-hour time formats. Depending on where you live, Windows might set the default time format to the 24-hour clock. If you don’t want to use the 24-hour clock, you can easily change the 24-hour clock to the 12-hour clock with just a few clicks.

Before proceeding, you should know that Windows uses two different formats called “Short time” and “Long time” to show the time. The “short time” appears on the taskbar to the bottom right corner. The “long time” appears in the calendar flyout that appears when you click on the taskbar clock. Since Windows treats them as two separate entities, you can configure them separately. For instance, you can show the 12-hour clock on the taskbar and a 24-hour clock in the calendar flyout menu.

Without further ado, let me show you how to change 24-hour clock to 12-hour clock in Windows 10.

Change 24 hour clock to 12 hour clock

The Settings app makes it quite easy to change the time format in Windows 10. All you have to do is select the 12-hour time format from a drop-down menu and you are good to go.

  1. Press Win + I to open the Settings app.
  2. Go to the “Time and Language” page.
  3. Select “Region” on the sidebar.
  4. On the right-panel, scroll down and click on the “Change Date Formats” link.
    How to convert from 24 hour to 12 hour time
  5. Select the 12-hour format time from the drop-down menu under “Short time“.
  6. Next, select the 12-hour format time from the drop-down menu under “Long time“.
    How to convert from 24 hour to 12 hour time

That is all, you will instantly see the 12-hour clock on the taskbar.

How to convert from 24 hour to 12 hour time

When you can click on the taskbar clock, you will see that the long time is also changed to 12-hour format.

How to convert from 24 hour to 12 hour time

Use Control Panel to Change 24 Hour Clock to 12 Hour Clock

You can use the good old control panel to change the time format from 24-hours to 12-hours. The good thing is that this method will work in all major Windows versions like 10, 8, and 7.If you like to use the Control Panel, follow this method.

  1. Open the “Start Menu“.
  2. Search for “Control Panel” and open it.
    How to convert from 24 hour to 12 hour time
  3. Select “Large Icons” from the top-left corner.
  4. In the Control Panel, find the “Region” option and click on it.
    How to convert from 24 hour to 12 hour time
  5. In the Region window, select h:mm tt from the “Short time” drop-down menu.
  6. Select h:mm:ss tt from the drop-down menu next to the “Long time” option.
  7. Click on the “Apply” and “Ok” buttons to save changes.
    How to convert from 24 hour to 12 hour time

That is all. The changes are saved instantly. You can see the changes reflect on the taskbar and in the time and date flyout that appears when you click on the taskbar clock.

How to convert from 24 hour to 12 hour time

As you can see, it is rather easy to change the time format from 24-hour clock to 12-hour clock in Windows 10 using the Settings app or the Control Panel.

I hope that helps. If you are stuck or need some help, comment below and I will try to help as much as possible.

This is a PHP tutorial on how to convert a standard 24 hour date and time into a 12 hour time. Furthermore, I will also show you how to add the AM and PM period abbreviations.

Take the following example:

In the code above, we converted a standard datetime string into a 12 hour time with an uppercase AM/PM abbreviation. We did this by using PHP’s inbuilt date and strtotime functions. The character “g” tells the date function that we want a 12-hour format of an hour without leading zeros. The uppercase “A” character is for AM / PM.

But what if you want a lowercase am / pm abbreviation?

As you can see, it’s pretty much the same as the first example. The only difference is that we used a lowercase a instead of an uppercase A in the format parameter.

Note that we removed the time in seconds from both examples as seconds are usually not typically displayed in this format.

Using the DateTime object.

If you prefer using PHP’s DateTime object, then you can use the following code:

The above piece of code will print out: 4:56pm

Leading zeros.

If you do want to display leading zeros in your time format, then you should use the character h instead of g.

If you run the PHP code above, you should see that it prints out: 09:12am

That’s pretty much all there is to it! Hopefully, this guide solved your problem!

Post by brave » April 27th, 2019, 12:30 am

How to convert from 24 hour to 12 hour time

Re: How do I change this 24 hour clock to 12 hour?

Post by eclectic-tech » April 27th, 2019, 2:44 am

You can do it by changing the [MeasureTime] line Format=%R to Format=%r .

You can use any combination of these Time Format codes to control how the time is displayed:
%H: Hour in 24-hour format (00 – 23)
%I: Hour in 12-hour format (01 – 12)
%M: Minute as number (00 – 59)
%p: AM/PM indicator for 12-hour clock
%r: Full 12-hour clock time. (e.g. “10:55:03 pm”)
%R: 24-hour HH:MM clock time. (e.g. “22:55”)
%S: Second as number (00 – 59)

I am not sure how your skin is using [MeasureTimeampm] since the time was set for 24 hour display; you may need to change other things if you end up with double AM/PM indications on the time display.

Re: How do I change this 24 hour clock to 12 hour?

Post by ms310 » April 27th, 2019, 2:46 am

I am no expert, but I tinker with a lot of time and weather skins.

The docs for Rainmeter are really awesome, with examples:

In this link you will see the following two entries:

In your case your current code is using %R for the format code. Change it to %r and see if that does the trick.

Converting 24 hour time to 12 hour time and a REGEX_Replace question

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I just wrote my first REGEX expression from scratch, well sort of, with help from all the documentation and posts and YouTube videos from @MarqueeCrew (the link to was great help) and the courage to try from @Joe_Mako but I’m still running into a bit of snag but hopefully I’ll sort it out eventually.

After searching the community I found posts regarding converting 12 hour time to 24 hour time but not the other way around. And after I used the 12 to 24 hour documentation to figure out the 24 to 12 path, I still had a client request to format the time a bit outside of normal parameters. they wanted it to be a.m. and p.m. super annoying but with Alteryx and REGEX problem solved. I don’t know if anyone else will end up needing something like this but I know I’ll forget and be searching for this in the future so this post is for me! The next step is to figure out how to make this all happen in one REGEX tool or formula tool.

First the conversion from 24 to 12 hour format was easily accomplished with the DateTime Tool and the Alteryx documentation on DateTime Functions when you hit the Specifiers drop down you get an explanation of all the options for date and time formatting in the DateTime Tool and you find the element that gives you the am or pm is the code %P for lower case am/pm and %p for uppercase, but you also have to swap out the usual HH for an %I (upper case i) or if you want to get rid of the leading 0 on the hours you can use %l (lower case L) which gets a little confusing because they look the same in the formula below but you can see in the tool a preview of the output.

A slight change in the query, try this:

convert ( varchar ( 2 ), datepart ( hour , getdate ()) % 12 ) + ‘:’ +
right( ‘0’ + convert ( varchar ( 2 ), datepart ( minute , getdate ()) ), 2 ) +
case when datepart ( hour , getdate ())> 12 then ‘ pm’ else ‘ am’ end

  • Marked as answer by Jinchun Chen Microsoft employee Monday, December 14, 2009 3:24 AM

All replies

We’ve actually recently had discussion about this issue. Check this thread – I hope it helps you. If not, let us know and we’ll do what we can.

  • Marked as answer by Jinchun Chen Microsoft employee Monday, December 14, 2009 3:24 AM

Could you clarify further of what you are trying to do here. You actually want 1:00 pm result instead of 13:00:00, be done in SP rather than in Reporting Services itself? Then you need to parse the time portion.

select convert(varchar(2),hour(datefield) % 12) + ‘:’ + convert(varchar(2),minute(datefield)) + case when hour(datefield)>12 then ‘pm’ else ‘am’ end

Edit: Sorry, I didn’t test the code supplied above. Try these instead:

select convert(varchar(2),datepart(hour,datefield) % 12) + ‘:’ + convert(varchar(2),datepart(minute,datefield)) + case when datepart(hour,datefield)>12 then ‘pm’ else ‘am’ end