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How to correctly calculate the rod spacings on a stacked roman blind

This guide covers how to calculate the number of folds needed for the length of your roman blind and how to work out the distance between the rods; it also covers how to work out how far up from the bottom of the blind to put the first rod to get the bottom ‘half-fold’ the correct size


It is a good idea to work out how many folds and roman blind rods you will have before you start making-up or even cutting your fabric. This will ensure that you have left yourself with the correct allowances for the top and bottom hem and enough length of fabric to achieve your finished length and desired number of folds (or maybe even a little margin for error if needs be).

The Bottom-Fold Myth!

It’s worth taking a moment here to discuss the bottom fold depth, as some guides advise that all the folds for a stacked Roman blind should be equally spaced. However, whilst this initially seems a sensible approach it actually has an undesired effect on the final look of your blind.

The way in which the operating mechanism raises the blind and folds the fabric, means that the bottom piece of fabric will stay flat and not fold. This means that it will overhang the bottom edge of the first pleat, rather than sit neatly behind all other folds and pleats. If this is a look that you desire then fine, it is OK to calculate and measure off your folds in this way. But, this method does increase the finished stack depth considerably and looks a little untidy and unbalanced in portion to the rest of the neatly and uniformly folded blind.

The correct way to calculate the roman blind rod spacings and fold depths is to aim to get the depth of the spacing for the first rod pocket (bottom fold) to be as close to half the depth of all the other full spaces as possible.


Step One:

To start with let's work out how many full and half folds you will require. You can do this using the simple to follow table below. This table is based on our own industry experience and recommendation of fold quantities. 

N.B. The first table (Roman Blind Kit Method) is to be used with roman blind kits, where you only have 5 rows of tape and 5 rods. If you are making a custom made blind and have access to more tape and additional rods for roman blinds then please use the second table (Custom Method).
N.B. The instructions provided with our roman blind kits may vary slightly from the instructions below, however the method below is an alternative approach that you may choose to use instead.
Roman Blind Kit Method
 Blind Length (upto) Blind Folds
24 inches / 61cms 2 full, 1 half
36 inches / 91.5cms 3 full, 1 half
48 inches / 122cms 4 full, 1 half
96 inches / 244cms 5 full, 1 half
Custom Method
 Blind Length (upto) Blind Folds
24 inches / 61cms 2 full, 1 half
36 inches / 91.5cms 3 full, 1 half
48 inches / 122cms 4 full, 1 half
60 inches / 152.5cms 5 full, 1 half
72 inches / 183 cms 6 full, 1 half
84 inches / 213cms 7 full, 1 half
96 inches / 244cm 8 full, 1 half


Step Two:

Next, to work out the size of your full and half folds simply:

  • Add 0.5 to the number of full folds. For example for a 24 inch blind (2 full folds, 1 half fold), add 0.5 to 2, to give you 2.5.
  • To work out the size of your full fold you need to divide your blind length by this number. For a 24 inch blind, you will divide 24 inches by 2.5. This gives you 9.6 inches for the length of each full fold. 
  • Then to get the size of your half fold, simply divide your full fold length by two. In this example divide 9.6 inches by 2, to get 4.8 inches
  • This give you 2 full folds at 9.6 inches, and 1 half fold at 4.8 inches. Just to be sure, add these numbers up and you should get the full length of your blind: 9.6 + 9.6 + 4.8 = 24

This calculation may look a little daunting at first, but if you follow the simple steps then you will get a well-proportioned and attractive looking blind. Plus doing the sums to begin with will definitely be less costly and time consuming than re-making your blind!

Here's another example with a 38 inch blind: looking at the table above you will see a 38 inch long blind has 4 full folds and 1 half fold. So we add 0.5 to 4, this gives us 4.5. We then divide 38 inches by 4.5, this gives us 8.44 (the size of our full folds). Then to get the size of our half fold, just divide 8.44 by 2, this gives us 4.22. To check that this is right we add everything together: 8.44 + 8.44 + 8.44 + 8.44 + 4.22 = 37.98. Not exactly 38 inches but 0.02 inches (half a millimetre)  is a good enough tolerance. 

  • Pro-Tip: If this is the first time that you’ve made a roman blind and you’re a little unsure whether the measurements that you’ve arrived at are going to look right, then make your blind up, lay it out on a flat surface such as a table or the floor and mark the measurements at the side edges of the blind with pins. Keep the pins close to the edge (particularly if your blind is blackout lined) so that you don’t leave any unnecessary pin holes in the fabric or lining. Temporarily form the folds by bringing the pins together one row at a time so that the folds stack on top of each other in turn. You should now be able to see how deep the folds look, what the finished stack will be and if the bottom half fold is the right depth. Remember you don’t want the bottom edge of the blind to disappear behind the bottom edge of the first full fold or to show too much below it. It needs to be level with the first full fold or showing no more than 2 cms below. If you’re not happy with any of the measurements or proportions then recalculate and repeat the pinning procedure again until you’re happy with the finished proportions.

Please remember that the maximum blind length/cord allowance on a cassette track is 8’ Foot or 96”/ 2.4 meters. 

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