You have two choices for lining up your AR-15 Iron Sights with your new favorite Red Dot or Holographic Sight: Absolute Co-witness or Lower 1/3 Co-witness. So, if you’re not sure how to set up these red dot sight configurations….and…you want the secret sauce for which co-witness to use? Follow along, we’ve got the answer.

Note: This article is focused on AR-15 setups that use red dot sights and backup irons, since this is the most popular configuration we see. But the concepts apply to any weapon where iron sights are used along with an optic.

Backup Iron Sights and Red Dot Sights

Red dot sights are one of the most popular sight options on modern weapons – offering both accuracy and speed of target acquisition. But like any battery-powered item, they can fail, so it’s wise to consider backup iron sights as added insurance.

Now, if you’re going to have two different sighting systems on your weapon, you’ll want to make sure they work harmoniously with each other.  This is where “co-witnessing” comes into play.

What Are Co-witness Sights?

Simply put – co-witness refers to the alignment of your iron sights with your red dot sights. If your irons and your optics are both sighted in, you would expect them to be aligned (co-witnessed) with each other when you line up your shot.

This is the basic concept, but in reality, it’s a bit more complicated because there are different varieties of co-witness sights that you can use.

On an AR, the two most common co-witness types are – “Absolute Co-witness” and “Lower 1/3 Co-witness“.

AT3 RD-50 Red Dot Sight FDE Co-witnessing with Magpul MBUS Backup Sights

Difference Between Absolute Co-witness and Lower 1/3 Co-witness?

The graphic above shows the difference between absolute and lower 1/3 co-witness on ARs with both optics and iron sights. If you are wondering where the best spot is to mount your red dot sight make sure to check out this article we put together to answer any questions you may have.

If you are looking for more information on adjusting your iron sights make sure to check out this FREE Official US Army Manual for AR15 / M4 / M16.

What Does “Absolute” Co-witness Mean?

This is the situation where your red dot optic and backup iron sights are mounted at the same height. If properly mounted the red dot should settle directly on top of the sight post and both the dot and sight post should be in the middle of the optic window.

Absolute Co-witness

What Does “Lower 1/3” Co-witness Mean?

This means that your red dot optic will be mounted higher than your iron sights. In this case, your iron sights will be in the lower 1/3 of your optic when you look at your dot in the middle of the optic window.

Lower 1/3 Co-witness

Control Your Type Of Co-Witness

This is all done with the height of your optic. Many red dot sights use riser mounts for this purpose – for example, the AT3 RD-50 PRO Red Dot Sight gives you a choice of mount heights.

  • Absolute co-witness – Optic is mounted at the same height as the iron sights or about 2.6″ above the center of the bore
  • Lower 1/3 co-witness – optic is mounted slightly higher than the iron sights or about 2.8″ above the center of the bore

There are advantages and disadvantages of each type of co-witness, which we break down in the chart below.

Absolute Vs Lower 1/3 Co-witness Sights Comparison Chart

Recommendations: Absolute Vs Lower 1/3 Co-witness Sights

So which setup is best for you? Keep in mind that either setup will work, so this really boils down to personal preference.

But we’re asked this question a lot, and this is what we recommend:

  • If you have flip-up iron sights – go with an absolute co-witness. Since you’re probably going to have the sights flipped down most of the time, you might as well have your red dot at the “standard height”
  • If you have fixed iron sights – we recommend lower 1/3 co-witness. This will give you an uncluttered view of the red dot, but you can still drop your line of sight to use the iron sights if needed.
  • If you don’t have iron sights – co-witness doesn’t technically apply, but when choosing the mount for your red-dot sight, go with an absolute co-witness sight setup, because it will put the optic at the “standard height” that the AR-15 was designed for.
AT3 Alpha Micro Red Dot w/ Riser. Perfect Optic for Co-witnessing!

One Last Tip

If there’s anyone that knows the AR-15 platform, it’s the US military. As a special offer for our readers, you can get the Official US Army Manual for AR-15/M4/M16 right now – for free. Click here to snag a copy.

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23 thoughts on “Absolute Vs Lower 1/3 Co-witness Sights -The Ultimate Guide [2024 Update]

  1. Just a question. If your RDS and back up rear I ron sight both fail (for whatever reason) can you use the the RDS aperture as “rear sight” if you are using absolute cowitness with the front sight? I reckon at 100-150 yards you will still hit a torso MOA.

  2. Recommendation for forward (Ultimak) mount on Yugo AK 47? I prefer absolute co-witness. Will I need the riser (.83” or 1”)???

  3. […] Mount Type: The interesting thing about this red dot scope is that it comes with a lightweight mount and armor. The mount is a Med 0.83” Pro-Mount Riser or Cantilever Mount. The purpose of this mount is to ensure adequate cowitness, as it is used alongside iron sights. […]

  4. Excellent explanation and illustration of the co-witness options for an AR15 novice. Thank you very much!

  5. I have a Springfield Saint Victor pistol and have a SigSauer Romeo 4 mounted on it. Which mount would you suggest? I like the Co-witness but not sure of which one to order. Like the idea of using both sights (Romeo and iron flip up sights) for longer distances. Any help would be appreciated. Thank you in advance.

  6. Thank you for your valuable information on this topic. I own a Smith & Wesson M&P 15 Sport II, and the front sight is not a flip-up one, but a fixed one. Only the rear sight is a flip-up. So I think I should go with the lower 1/3 cowitness, in order not to clutter the view of the red dot…
    If I get it correctly, I should buy a Hi Profile 1″ Riser mount…. is it correct?
    Thank you!

    1. Yeah that’s my question too. My Colt’s M4 has a fixed front sight with flip up rear sight. Should I use the absolute co-witness or one-third with my hybrid set up??Vortex scope also btw on my patrol rifle.

  7. Thank you for your wisdom and clarity on absolute,.

  8. If you have fold down BUIS, go with absolute.

  9. I am running into an issue where unless I use a riser on my red dot my iron sights co-witness in the top 2/3 of the scope. I’ve seen this with a few different red dots. And I cannot find a 1/4″ riser that will get me into an absolute co-witness.

  10. What would the formula be for a carbine with an a2 carry handle?

    1. Buy a at handle mount for the red dot, cheek weld probably wont be much if its mounted lower 1/3.

  11. Good Article, and well written for the AR Newbie and those considering eith a Red Dot or Iron Sights. The diagrams you supplied gave a good visual representation as well. Having the Pros and Cons of each type of system is a big help.

  12. Thank you for such a clear definition of
    co-witness, which would you recommend for use on a flat top using HK iron sights?

  13. Thank you for a easy to understand, but fully informative article. Sound advice!

    1. I am still confused… I have a S&W M&P 15 Sport II with a flip down rear sight and a fixed front sight. What is best for this setup–absolute or 1/3 co-witness? I have never used a reflex sight and I am looking at the Holosun 510C since it allows, I presume, a greater field of view than a barrel tube sight like an Aimpoint Pro or Sig Sauer Romeo 5. I live in a desert environment and many backdrops are tan colored buildings and desert scape. So another factor is red vs. green dots. Thoughts and considerations?

      1. I’d go with absolute cowitness since you will have the rear sight flipped down most of the time. It can also help with quicker target acquisition since the front sight post lines up with the dot.

      2. I have a sport 2 with a romeo 5 setup. The absolute setup, in my opinion, is the most effective. I’ve tried multiple setups with different guns and sights over the years, and in a tight spot, it’s just a natural instinct for your eyes to focus to a single point. I noticed that when aiming quickly for a target, when they are absolute, at least your iron and dot are fixed on a single point, and I personally could get the shot off faster and more accurately without having to think about which sight to focus on. As far as red vs green, in your area, the green will stand out a lot better. I am in east TN, where everything is green, lol so red obviously works better for me in the outdoors.

      3. Go with a lower 1/3rd, this way the front sight is out of the way.

      4. Use info for front sight as this is the one you are using to use with your red dot. Use absolute as your front iron sight doesn’t move. I also live in a desert landscape and personally have found red dots to stick out more than green as green seems to still get lost more often. Your eyes are drawn more often to red because of your primal instincts (food, danger).

    2. Use info for front sight as this is the one you are using to use with your red dot. Use absolute as your front iron sight doesn’t move.

  14. Hey Hugh, I would recommend running it without a riser on the mini-14, that’s how most people tend to run red dots on those. If you have any more questions, let us know!

  15. Good day good info I put your AT3 red dot on a Ruger 556 (absolute ) works great want to put one on an early mini-14 what would your advice be for a mount? thanks

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