It's something, not sure about "correct". 
That will add the remainder of width divided by 16 (between 0 and 15) to the width, which now that I think about it more isn't quite what you want. Give this a whirl:
width += 16 - (width % 16);
height += 16 - (height % 16);That should be the right math. There's still some question as to exactly where to add it in the code, and if any other code needs to be adjusted, but give that a try in the same place.
Hey @Nate, that worked but didn't ignore layers that were already divisible by 16.
I also noticed that layers with the [scale] tag were not divisible after export. For example, after exporting with your amended script a layer's width was 80px. Divided by 16 this is 5 so that's correct. However I applied a [scale:0.5] tag to the layer and re-exported. The width was now 40px and when divided by 16 is 2.5.
I fear this requires a lot of adjustment in the code! 
% is modulo. 40 % 16 gives 8 because you effectively subtract 16 until you have < 16, so: 40 - 16 - 16 = 8. 16 - (40 % 16) also gives 8. That means 40px would become 48px, which is correct (so far).
Later we do width * scale, which is the [scale:x] value. For that to work you probably want:
width += (16 - (width % 16)) / scale;
height += (16 - (height % 16)) / scale;Dictated but not read. 
Hey @Nate, thank you for explaining. On the weekend too!!
The code is working in general for making all exports divisible by 16, however layers with [scale] tag & layers already divisible by 16 are not being affected as desired.
I've opened a massive can of worms here!
What happens with layers already divisible by 16? They should be exported as normal, since the math evaluates to zero.
Hey @Nate, there's a layer that is already divisible by 16 but that layer is also having pixels added on.
The original size is 896x896 but is being exported at 912x912.
Here are my settings in the script panel, could it be the default padding of 1px that is throwing it off?
Massive thanks! Steve
I tested exporting with Padding set to 0px and it has caused the "divisible by 16" code to now be ignored.
Does the padding need to be set to at least 1px for it to work?
Cheers, Steve
Try this to account for padding:
width += (16 - ((width - settings.padding * 2) % 16)) / scale;
height += (16 - ((height - settings.padding * 2) % 16)) / scale;Nothing is ignored, the math just works out to zero when width - settings.padding * 2 is divisible by 16. Ah actually it works out to 16 - 0 = 16. You can try:
var increase = (width - settings.padding * 2) % 16;
if (increase > 0) width += (16 - increase) / scale;
increase = (height - settings.padding * 2) % 16;
if (increase > 0) height += (16 - increase) / scale;Nate
Hey Nate, I tried your first suggestion and it made the 896x896 layer 914x914 this time.
Trimming was set to 1px.
tried your second suggestion too, this time it's changed the 896x896px layer to 989x989px.
Trim padding was set to 1px again.
In both cases, if trim padding is set to 0px then the script seems to ignore the divisible part!
Apologies for taking up your time on this, I appreciate you help
For 896 with 1 padding increase is zero and nothing should change. Nothing we did can change 896 to 989, which is a difference of 93. The most we add is 15 / scale. Maybe something is going on with scale. Remove your scale tags or remove / scale and see. Use alert so you can see the values, ie alert(increase);.
Hey @Nate, thanks again for your help. I tried removing the scale tags and /scale but it's still returning strange results.
After running the script with padding set to 1px, the layer that's 896x896 has exported at 898x898. Adding on 2px rather than ignoring this layer.
Not sure if you have time but would you mind checking the PSD & script i've attached? No problem if you haven't got time. Very grateful for your help so far 
896 to 898 is correct. Wait, you want to not export layers that are divisible by 16? I missed that requirement. Try:
var increaseX = (width - settings.padding * 2) % 16;
if (increaseX > 0) width += (16 - increaseX) / scale;
increaseY = (height - settings.padding * 2) % 16;
if (increaseY > 0) height += (16 - increaseY) / scale;
// Save image.
if (writeImages && (increaseX || increaseY)) {That will skip create the image. I guess that's what you mean by ignore? It'll still be in the skeleton data as an attachment.
I didn't try the PSD because it seems like the problem was in defining the requirements rather than the code. Hopefully the above is enough. 
Hey Nate,
Apologies if i've not been clear, my original request was to still export those layers that are divisible by 16, but not add any extra padding.
- Check if a layer's dimensions are divisible by 16, if not then add on padding to make it divisible by 16 & export png as normal
- Check if a layer's dimensions are divisible by 16, if it is then ignore padding and export as png as normal
I still tried your suggestion above that ignores those images, however the results are again returning weird values. For example, with padding set to 1px, an indivisible layer with dimensions 506x658px is exporting at 514x674px.
With padding set to 0px the layer exports at 506x658px again, ignoring the code.
Also, should there be a var at the start of this line in the code? -
increaseY = (height - settings.padding * 2) % 16;