How to Calculate the size of curtains for your windows
Calculating curtain fabric is an art of precision, ensuring your windows don’t just get covered, but are framed with elegant, abundant folds. Curtains can make or break a room’s design, but measuring them is where most people get tripped up. Do you measure the window? The rod? The floor?
Before we dive into the math, here’s how we establish our base measurements and set the stage for luxurious drapes.
Step 1: Defining Your Dimensions
The first critical step is capturing the width and the exact height you desire for your curtains.
The width is pretty simple. Measure the width of the curtain rod or curtain box.
Your curtain’s final height is influenced by two main factors:
- The Termination Point- Where do you want the curtain to land? For the most optimal appearance:
- You can let the fabric gather luxuriously on the floor (adds drama, requires more length).
- You could choose to have the curtain just touch the floor (at the skirting board).
- Terminate the curtain about 1.5 cm or ½ inch) above the floor for a neat, dust-free look.
This is a style choice, but the measuring point is crucial. I always recommend measuring from the top of your curtain rod/track.
(PRO TIP): Always measure your length in at least three places—left, middle, and right. Floors and walls are rarely perfectly straight. Use the shortest measurement to prevent your curtain from dragging.
- The Heading Style such as pencil pleats, eyelets/ grommet, rod pocket, pinch pleats etc might need different allowances.
For this case, I will use the hover/kiss right before the skirting as my termination point & Eyelet or otherwise known as a grommet as the heading style.
NB: Keep in mind that some curtain rods have a support bracket or joint in the middle. This joint prevents you from smoothly pulling a single curtain (like a sheer panel) all the way across the rod. If your rod has a joint, you will need to purchase the sheer and curtain in two separate pieces.
Step 2: Your Window Inventory
Get your tape measure out, a notepad, and let’s get started! Now I have taken measurements for the three windows that I am going to use as an example and the results are as follows:
- Living Room window
Width= 270cm / 2.7m
Height= 225cm / 2.25m
- Living Room Door
Width = 110cm/ 1.1m
Height= 225cm/ 2.25m
- Bedroom Window
Width = 200cm/ 2m
Height= 223cm/ 2.23m
Step 3: The calculations
- Deciding on Fullness (Gathering)
Now that we have our window measurements, the next step is deciding on the curtain material width, which determines the look and fullness of your gathers. For that polished, professional style, whether you want a few soft folds or a rich, abundant gather – I recommend material that is 2.5 to 3.5 times the width of your rod.
Personally, my standard sweet spot is 3 times your rod width for the perfect fullness.
- Hem and header allowance
The fabric you cut must be longer than the finished length to allow for folding and sewing at the top (header) and bottom (hem).
We’ll add a generous 20cm to the length, 10cm for the top header and 10cm for the bottom hem).
Example: The required cut for the Living Room Window will be 225cm + 20 cm= 245cm
You can take a shortcut: multiply the width of your window by three to find the needed fabric width. Crucially, this method only works if the total length of your finished curtain, including the hem/header allowance, does not exceed the standard length of the material. (Here in Kenya, that’s typically 280 cm to 300 cm). Common Standard Widths: 137cm, 182cm, 228cm and 280cm
With the window we just measured for instance, our length of 225cm. If we add 20cm allowance for header and hem, it is still below 280 cm so we can safely use the width, multiply it by 3 to determine the fabric size.
However, there are two scenarios where the shortcut won’t cut it:
i. When your window length is longer than the standard fabric length, or
ii. You simply prefer to calculate the exact fabric size for precision.
For these cases, I’ll be sharing a formula to use shortly, and we will apply it now to the windows we just measured.
For our example, we will proceed using a popular extra-wide fabric with a standard width/height 280cm (often “railroaded” where the 280cm becomes the curtain height).
3. The formula
Total fabric (m)= [(Ww×F)×(Hw+Ah)]/ (Wf×100)
Where:
- Ww = window width (cm)
- Hw = window height (cm)
- f = fullness ratio (e.g. 3 for triple fullness)
- Ah = allowance for hems/headers (cm)
- Wf = fabric width (cm)
Let’s plug in the numbers now, beginning with the living room window.
Given (Living room window)
- Ww = 270cm
- Hw = 225cm
- f = 3
- Ah = 20cm
- Wf = 280cm
Total fabric (m)= [(270×3)×(225+20)]/ 280*100 = (810 x 245)/28,000= 7.1m
..Then we’ll quickly move on to the living room door,
Given (Living room door):
- Ww = 110cm
- Hw = 225cm
- f = 3
- Ah = 20cm
- Wf = 280cm
Total fabric (m)= [(110×3)×(225+20)]/280*100= (330 x 245)/ 28,000= 2.89m
…and finally, we’ll calculate the needs for the bedroom.
Given (Bedroom window):
- Ww = 200cm
- Hw = 223cm
- f = 3
- Ah = 20cm
- Wf = 280cm
Total fabric (m)= [(200×3)×(223+20)]/(280 x 100) = (600 x 243)/ 28,000= 5.21m
Notice that the only thing we alter in the formula is the Window’s width and Height? That’s because the desired results and the material width remains the same across.
Supposing the height of the curtain material was 137cm not 280cm, then the total fabric required for the living room window would have been:
Total fabric (m)= (270×3)×(225+20) = 810 x 245 = 14.49m
Now I’ll head out for the curtains shopping to show you the final look so don’t leave yet. The client wanted something heavy and subtle in color for the living room and a slight pop for the bedroom so I picked this shade of blue for the bedroom & the light pink that is almost invisible for the living room.
If this guide was helpful, hit that like button. Let me know in the comments: Are you a ‘Kiss’ or a ‘Puddle’ person?
