How Much Blur? – A Bokeh Calculator

One of the most returning questions on photography forums is which out of two different lenses has the smallest depth of field (DOF). However, what many people actually mean when they ask this is which lens has the best ability to blur the background in their shots. The answers given are not always very clear. However, they could be just that. All it takes is some simple math. This bokeh calculator will give you the answers you are looking for. Add some lenses, select your subject size, and hit update to see the results in a graph!

Add some more

I want to take a shot in landscape orientation, which contains someone's head and shoulders (0.9 x 0.6 meters), a full person (3 x 2 meters), or something completely different, which has a width of meters.


Background blur versus background distance

Theoretical blur disk diameter as percentage of image width [%]

Generated by

Distance between subject and background

With this nice little slider you can set the distance range of the graph:

It is important to intepret the results correctly. The first obvious observation to make is that the background blur increases when the background is further away, regardless of focal length or aperture settings. In order to give meaning to the results, think about what kind of shot you want to make, and what distance there will be between the subject and the background.

As you probably have seen by now, the relative blurring ability of lenses is very much dependent on the specifics of your shot. As a rule of thumb it can be concluded that a wider aperture is more important for blurring closer backgrounds, whereas the focal length comes more and more into play when the background is further away. Please note that there are two additional effects which determine the amount of background blur in your shot:

  1. Each lens has its own bokeh characteristics, which can make background blur appear more or less smooth.
  2. A shorter focal length will have a wider field of view, and therefore it is likely that there will be more objects in the background at a closer distance.

You can always link back to this specific comparison by using the following url:

This is version 2.0 of how much blur. Stay tuned for more features and photography greatness. You can always send your suggestions to . And no, I do not support my growing family through this website!

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  • Malex

    Great tool, thanks!

  • Malex

    how should I enter info for a lens on a micro four third body with a metabone adapter ?
    let’s say the x0.71 Ultra adapter with the Sigma 18-35mm f1.8 on the GH5
    the crop factor becomes 1.42 (2 x 0.71) but how about the Fstop, should we multiply it also (1.8 x 0.71 = 1.27) ? or should I leave it as f1.8 ?

    • I am not familiar with that particular adapter, but if you compensate the crop factor with the 0.71 to 1.41, you should enter the lens characteristics unmodified. Hope that helps.

    • Hal Knowles

      @Malexirian:disqus as focal reducing adapters, the Metabones Speedboosters add 1 stop of extra light gathering capability to the adapted lens. So using the one quarter f-stop scale, an f-stop of 1.8 would become an f-stop of 1.3 with the Speedbooster. In my personal experience a Canon 50mm f1.8 lens appears in my EXIF data as a 35mm f1.3 when adapted on a GH5 with a Metabones Speedbooster. So on this tool, I would enter the 35mm f1.3 data plus a crop factor of 2 (or conversely, as you suggested I could use the original 50mm plus a crop factor of 1.42).

  • DanR

    Fantastic! I was on the fence about buying the Panasonic 42.5mm F1.7 lens for my G85 camera but this confirmed what everyone is saying about it and I pulled the trigger. Thank you so much!

  • John Morgan

    This is a GREAT program, and one sorely in need of showing to people.

    But, respectfully, your analysis of what most affects bokeh at the end was not correct.
    I will use this very program with 9 (made-up) lenses to show what is correct.
    First, copy the following line and open a web page with it to start this program with the 9 lenses:

    You will see a pretty graph with 9 different lines. The lens values for crop factor, focal length and f/# are values chosen to show what really matters for bokeh very near and very far from the subject. They aren’t for real lenses, just so you know. (If you want to prove my results for real lenses, feel free to try any lens combinations and you’ll see it holds true)

    Now set both sliders for the distance range (at the bottom) to the left (for 1 to 2 cm). Notice that there are now only 3 lines visible. These lines (from top to bottom) are for lenses with crop factor * f# = 6, 8, and 12. Therefore crop factor * f# is what matters for backgrounds extremely close to the subject. I like to call this the EQ f# (for the 35mm equivalent f# with respect to bokeh). It doesn’t matter what the lens focal length is!

    Now set both sliders for the distance range to the right (for 7 to 10 km). Notice that there are now only 3 (different) lines visible. These lines (from top to bottom) are for lenses with focal length / f# = 36, 24, and 12. Therefore focal length / f# (which is the maximum aperture) is all that matters for backgrounds extremely far away from the subject. It doesn’t matter what the crop factor is! And lens focal length alone is not what matters since when lenses have really big focal lengths they also have to have big f#’s in order to keep the aperture size reasonable and keep costs down. To re-emphasize this: When the background is extremely far away, the only thing that matters is the maximum aperture, and the sensor size makes no difference!

    Now set the distance ranges from 1cm to 10km. Notice that the 3 lines on the left (each with 3 lenses based on EQ f#) split up into 9 different lens lines, which then re-converge to 3 new lines (each with 3 lenses based on aperture) at the right. So bokeh size, from near to far background, varies from EQ f# smoothly to aperture size.

    Hope this helps, and thanks again to those who built this great program for us!