Density Altitude

[Lunar95]

So I have a vague idea what density altitude is.

Its a combination of a majority of external factors like altitude, temperature, pressure and few other to simulate an altitude that would equate to all these combined.

What I don't know is how to get it, either through math or some gizmo gadget, can someone point me in the right direction?

 

[6.5SH]

As to gadgets the main ones are Ballistic model Kestrel weather meters or the D3 Drop.

If you have a smartphone and data service available where you are shooting there are several online calculators that can be used:

DA calculator « Air Density Online

Real-time weather for racers including air density and density altitude. Over 1000 tracks and adding more every day.

airdensityonline.com

Density Altitude Calculator - English/Metric, Relative Humidity

A longer article that goes into the equations:

Equations - Air Density and Density Altitude

Calculation of Air Density and Density Altitude. Based on the 1976 International Standard Atmosphere. Includes javascript calculators.

wahiduddin.net

Keep in mind that most ballistic calculators have the ability to use the temperature, pressure/altitude and humidity values directly. So trying to convert all that by hand or on another site to enter one number is going to be slower.

There is value knowing how to do the math especially if you are using printed dope charts with a DA column.

EDIT:
Great article by @Jack Master demonstrating how to use DA without a Kestrel.

Understanding your Ballistics Calculator Atmospherics

Follow Sniper's Hide and pick up the latest information on all things precision rifle related. Sniper's Hide Training is for the serious tactical marksman.

www.snipershide.com

 

[_Windrider_]

You can get a kestrel. Easiest as it’s all done for you. There are simple density altitude charts available or you can memorize a few easy. Numbers and always be within a couple hundred feet of actual DA. The good news is with DA, rounding to the nearest 1000 is more than acceptable so the difference between 3700 DA and using 4000 is non existent.

first and foremost standard atmosphere is 59 F 29.92 in Hg pressure and 0% humidity. So at sea level at exactly those conditions your DA equals 0 as well as your elevation. Temp has a standard lapse rate of approximately 3.5 degrees F per 1000 feet of elevation gain and a standard pressure lapse rate of 1” Hg per 1000 feet. DA increases approximately 1000’ for every 15 degrees from the standard at a given elevation.

So at for example 4000 feet, if the conditions were 45 F and 25.92 in Hg your DA and elevation would be equal (I’m ignoring the effect of humidity. It’s irrelevant for our purpose). If the temp was 60 degrees your DA would be 5000 feet.

does that make sense?

for more accurate calculations accounting for pressure changes use this

here are the standard atmosphere numbers for the hasty method I showed above

or just save yourself the headache and carry this

 

[OREGUN]

Here’s a formula if you are a mathematician/physicist.

There’s a chart for quick and dirty calls if the effects of humidity aren’t terribly concerning to you.

DenAlt is pressure altitude corrected for nonstandard temperature...and is effected to a much lesser extend by humidity. Hot and humid is a higher DenAlt than cool and dry.

An online calculator or kestrel is a good choice.

 

[Hogrider2000]

A Kestrel is the way to go
and remember to change batteries often.
You do not need to use it daily unless radical weather changes--and then the tent is good!!!!!!!

 

[Baron23]

So I have a vague idea what density altitude is.

Its a combination of a majority of external factors like altitude, temperature, pressure and few other to simulate an altitude that would equate to all these combined.

What I don't know is how to get it, either through math or some gizmo gadget, can someone point me in the right direction?

It is, specifically, pressure altitude corrected for non-standard conditions. There is an ICAO model that defines pressure and temperature drop with increments of increasing altitude. Pressure altitude is the altitude that a given atmospheric pressure is to be found IAW this standard model.

 

[Rob01]

So I have a vague idea what density altitude is.

Its a combination of a majority of external factors like altitude, temperature, pressure and few other to simulate an altitude that would equate to all these combined.

What I don't know is how to get it, either through math or some gizmo gadget, can someone point me in the right direction?

Don't get too hung up on it. If you have a ballistic program that allows you to enter all the parts of DA individually you will get the same results as the program uses them to figure it all out.

 

[79steeler]

I thought Density altitude is what was happening to my brain as I get older??

 

[Yondering]

As to gadgets the main ones are Ballistic model Kestrel weather meters or the D3 Drop.

If you have a smartphone and data service available where you are shooting there are several online calculators that can be used:

DA calculator « Air Density Online

Real-time weather for racers including air density and density altitude. Over 1000 tracks and adding more every day.

airdensityonline.com

Density Altitude Calculator - English/Metric, Relative Humidity

A longer article that goes into the equations:

Equations - Air Density and Density Altitude

Calculation of Air Density and Density Altitude. Based on the 1976 International Standard Atmosphere. Includes javascript calculators.

wahiduddin.net

Keep in mind that most ballistic calculators have the ability to use the temperature, pressure/altitude and humidity values directly. So trying to convert all that by hand or on another site to enter one number is going to be slower.

There is value knowing how to do the math especially if you are using printed dope charts with a DA column.

EDIT:
Great article by @Jack Master demonstrating how to use DA without a Kestrel.

Understanding your Ballistics Calculator Atmospherics

Follow Sniper's Hide and pick up the latest information on all things precision rifle related. Sniper's Hide Training is for the serious tactical marksman.

www.snipershide.com

This is the easiest density altitude app I’ve found, and it uses the internal barometer in the phone rather than a weather service for pressure. Temp is easy to estimate closely enough for shooting even if you don’t have service.

https://apps.apple.com/us/app/density-altitude/id994402197

 

[_Windrider_]

This is the easiest density altitude app I’ve found, and it uses the internal barometer in the phone rather than a weather service for pressure. Temp is easy to estimate closely enough for shooting even if you don’t have service.

https://apps.apple.com/us/app/density-altitude/id994402197

Barometer plus is good too. And free

 

[Yondering]

Barometer plus is good too. And free

I have Barometer Plus as well but never use it; it just gives you pressure instead of a direct density altitude reading. That’s why I switched to Density Alt in the first place.

I guess they must have dropped the free version of Density Alt, but the paid version is definitely worth a few bucks.

Kind if like GPS units, the value of a Kestrel has waned for me with good apps that can do the same job without needing a separate device. Wind speed is the holdout of course, and I haven’t tried any of the units that connect to the phone because at that point I’m already carrying another device.

 

[Lunar95]

Ya'll nailed it.

Iv avoided a kestrel for about a yr now because i'd rather know how to do something before having something do it for me, chances are that ill pick one up in the coming months for some PRS matches and MSC anyways.

Appreciate the graphs and quick generic math its what i was looking for aswell, huge help.

 

[acudaowner]

 

[beetroot]

Why would use use density altitude rather than just use the measure Barometric Pressure?
Both ways will give you the same answer but if your Kestrel/Phone gives you Hg/hPa/millibar just put that in directly and don't worry about DA.

Unless I'm missing something (very likely).

 

[_Windrider_]

Why would use use density altitude rather than just use the measure Barometric Pressure?
Both ways will give you the same answer but if your Kestrel/Phone gives you Hg/hPa/millibar just put that in directly and don't worry about DA.

Unless I'm missing something (very likely).

DA is what I use for hasty field cards If I need a quick solution. If I have the time I always pull the kestrel out and get the exact environmentals. DA has its place And use.

 

[beetroot]

DA is what I use for hasty field cards If I need a quick solution. If I have the time I always pull the kestrel out and get the exact environmentals. DA has its place And use.

That's what I figured.
Do you use just ambient temp to estimate DA and ignore humidity?

 

[308pirate]

You can get a kestrel. Easiest as it’s all done for you. There are simple density altitude charts available or you can memorize a few easy. Numbers and always be within a couple hundred feet of actual DA. The good news is with DA, rounding to the nearest 1000 is more than acceptable so the difference between 3700 DA and using 4000 is non existent.

first and foremost standard atmosphere is 59 F 29.92 in Hg pressure and 0% humidity. So at sea level at exactly those conditions your DA equals 0 as well as your elevation. Temp has a standard lapse rate of approximately 3.5 degrees F per 1000 feet of elevation gain and a standard pressure lapse rate of 1” Hg per 1000 feet. DA increases approximately 1000’ for every 15 degrees from the standard at a given elevation.

So at for example 4000 feet, if the conditions were 45 F and 25.92 in Hg your DA and elevation would be equal (I’m ignoring the effect of humidity. It’s irrelevant for our purpose). If the temp was 60 degrees your DA would be 5000 feet.

does that make sense?

for more accurate calculations accounting for pressure changes use this

View attachment 7627348

here are the standard atmosphere numbers for the hasty method I showed above

View attachment 7627349

or just save yourself the headache and carry this

View attachment 7627350

Damned aviators................

 

[308pirate]

Why would use use density altitude rather than just use the measure Barometric Pressure?
Both ways will give you the same answer but if your Kestrel/Phone gives you Hg/hPa/millibar just put that in directly and don't worry about DA.

Unless I'm missing something (very likely).

Kestrels and phones die

DA charts always work and they are more than close enough.

 

[Yondering]

Why would use use density altitude rather than just use the measure Barometric Pressure?
Both ways will give you the same answer but if your Kestrel/Phone gives you Hg/hPa/millibar just put that in directly and don't worry about DA.

Unless I'm missing something (very likely).

Because you need at least 3 measurements to estimate DA - pressure, altitude, and temperature. DA combines all of that into a single number, and is simpler. (Of course truly accurate DA measurements are more complicated than that, but we don't need to be that precise.)

If you are trying to only use pressure alone, you're definitely missing something because it's not enough info.

 

[Yondering]

Kestrels and phones die

DA charts always work and they are more than close enough.

That has nothing to do with it. Do you understand what DA is? It's not just altitude.

How would you know what the DA is without some sort of device to measure and calculate it? Doesn't matter whether you have charts if you don't know what the number is in the first place.

 

[theLBC]

such awesome answers make me proud of you guys!

i look through this thingy and it tells me what to do based on where i am standing.

 

[theLBC]

That has nothing to do with it. Do you understand what DA is? It's not just altitude.

How would you know what the DA is without some sort of device to measure and calculate it? Doesn't matter whether you have charts if you don't know what the number is in the first place.

hahaha, lighten up. he's just saying that (excluding the extremes) whatever dope you're using is going to be close, give or take.
ice storm at or below sea level vs summer day at frank's place is completely different.

 

[Yondering]

hahaha, lighten up. he's just saying that (excluding the extremes) whatever dope you're using is going to be close, give or take.
ice storm at below sea level vs summer day at frank's place is completely different.

Nothing to lighten up about, chill out yourself. Someone asked for information and he gave bad info. Correcting it doesn't mean I'm worked up, and his response gave no indication that he actually understands DA.

What you're saying isn't fully accurate either and can vary a lot depending on location. It's not uncommon to see 4,000+ ft of DA change at one of my shooting spots for example between different visits, or a little less just between early morning and mid-day. Other places it stays more constant, but without a way to measure it or the necessary details, how would you know? True we don't need to be very precise, I like my DA cards in 2,000 ft increments, but the point stands that you still need some way to have a general idea what it is, and that doesn't just go by altitude and temp.

 

[theLBC]

Nothing to lighten up about, chill out yourself. Someone asked for information and he gave bad info. Correcting it doesn't mean I'm worked up, and his response gave no indication that he actually understands DA.

What you're saying isn't fully accurate either and can vary a lot depending on location. It's not uncommon to see 4,000+ ft of DA change at one of my shooting spots for example between different visits, or a little less just between early morning and mid-day. Other places it stays more constant, but without a way to measure it or the necessary details, how would you know? True we don't need to be very precise, I like my DA cards in 2,000 ft increments, but the point stands that you still need some way to have a general idea what it is, and that doesn't just go by altitude and temp.

correct answers were provided already, were they not?
of course, depending on caliber, conditions, target size, distance, contest, hunting or fun..., these things are more or less critical.
i am not saying you are wrong, i am just saying there is room for the "does it really matter?" question because we see folks get too wrapped up in the fine details instead of shooting. i defended it because i am somebody that likes a well set table before eating but learned that it doesn't matter one fucking bit if you can't cook for shit.

 

[_Windrider_]

That has nothing to do with it. Do you understand what DA is? It's not just altitude.

How would you know what the DA is without some sort of device to measure and calculate it? Doesn't matter whether you have charts if you don't know what the number is in the first place.

the effect of pressure on DA is negligible compared to temperature. if you know your approximate elevation, you can just use the standard pressure for that altitude and correct it for non-standard temp. its more than close enough.

 

[308pirate]

That has nothing to do with it. Do you understand what DA is? It's not just altitude.

How would you know what the DA is without some sort of device to measure and calculate it? Doesn't matter whether you have charts if you don't know what the number is in the first place.

I've been an FAA rated private pilot since 1997. I've also been shooting long range rifles in one form or another since 1999.

I know what DA is, likely much better than you do.

But thanks anyway.

 

[beetroot]

Because you need at least 3 measurements to estimate DA - pressure, altitude, and temperature. DA combines all of that into a single number, and is simpler. (Of course truly accurate DA measurements are more complicated than that, but we don't need to be that precise.)

If you are trying to only use pressure alone, you're definitely missing something because it's not enough info.

EDIT: having done my own research air density is a function of both pressure and temperature (I did know that...).
Which puts this discuss into context for me.

 

[fdkay]

I thought Density altitude is what was happening to my brain as I get older??

No, that's density ATTITUDE

 

[fdkay]

I will say, here at the coastal bend area of South Texas, we have extreme swings in DA.
One of our local airports used to report it.
Our actual altitude is around 25 feet ASL.
I have seen our DA go from 500 feet below sea level to 2500 feet above in a matter of a few hours.
It definitely affects your dope.

 

[Yondering]

I've been an FAA rated private pilot since 1997. I've also been shooting long range rifles in one form or another since 1999.

I know what DA is, likely much better than you do.

But thanks anyway.

Then you should have been able to answer the question that you attempted to.

I don't care how much you know something; if your comments indicate that you do not, whether through lack of information or just plain bad communication, don't be surprised if someone asks about it.

 

[Yondering]

correct answers were provided already, were they not?

By who? A question was asked, and neither of the other people replying to beetroot answered it, and in fact both replies were misleading to indicate that DA is just an approximation of the exact environmentals, when in reality it gives you the same answer and requires the same tools to measure the environmentals either way.

I'm genuinely interested to know which comments you thought actually answered the question that was asked. I'm guessing both of these people are capable of forming a good answer, but their communication sucks, as does yours.

 

[_Windrider_]

That's what I figured.
Do you use just ambient temp to estimate DA and ignore humidity?

Yes. Humidity effects are negligible. in all my solutions devices field cards or whatever, I just assume humidity is 50% and leave it. It cuts any error in half and is so small it doesn’t matter. If I was shooting Ko2m I’d be more precise.