How to Measure Windows for Double Curtain Rods

Key takeaways

• Measure the full window frame width, then add extra on each side (usually 10–20 cm) so curtains can stack off the glass when open.
• Use a simple formula: Rod length = Window width + Left overhang + Right overhang for both inner and outer rods.
• Mount double rods higher than the frame (about halfway between frame top and ceiling) to make windows look taller and allow for tall curtains.
• For wide openings or patio doors, choose sturdy adjustable sets such as an extendable double curtain pole that covers your full measured span.
• Always check bracket position, wall obstacles and the projection of both rods so curtains can move freely without hitting handles, radiators or blinds.

Why measuring matters for double curtain rods

Double curtain rods look elegant and are incredibly practical, but they are less forgiving than single rods when it comes to measurements. With two rods running parallel, there is more hardware on the wall, more fabric involved and more potential for things to look cramped or out of proportion. A rod that is too short can make your window seem smaller, while one that is too long may overwhelm the wall or run into nearby wardrobes, alcoves or shelves.

Accurate measuring also ensures your curtains actually work the way you want them to. The sheer layer should glide smoothly behind your main curtains without snagging, and both sets should close completely over the glass for privacy and insulation. If you misjudge the width, you might end up with a gap in the middle where light creeps through, or so little overhang that your curtains can’t stack neatly off the window during the day.

Double rods also add extra depth to the wall, which means bracket placement and height become more important. You need enough space above and to the sides of the frame not only for the finials but also for the bracket bases and the projection of the rear and front rods. Careful measuring helps you avoid awkward clashes with architraves, trims, blinds, cupboards or radiators.

Tools and preparation before you start

Before you begin measuring, gather a few basic tools and make a quick checklist of what you are trying to achieve. Spending a couple of minutes on this step makes the process smoother and reduces the chance of mistakes.

• Steel tape measure (at least 3–5 metres for wide windows)
• Pencil and paper or a printable worksheet
• Step stool or small ladder for tall windows
• Spirit level (optional, but helpful for checking existing frames)
• Helper for large patio doors or very wide spans

It can help to sketch your window roughly and label the key parts: frame width, desired overhang on each side, and approximate mounting height. You can create a simple worksheet by drawing three boxes: one for a standard window, one for a tall or floor-length window, and one for any sliding or patio door. Under each, add lines for window width, overhang left, overhang right, rod length and mounting height. Fill in the numbers as you go.

Also decide which type of curtains you are planning to use on each rod. Eyelet curtains, tab tops and pencil pleat headings all hang slightly differently. If you are opting for a ready-made double rod set such as a nickel extendable double window pole, check its minimum and maximum length so you know your measurements fall comfortably within that range.

Step 1: Measure the actual window width

Start with the simplest measurement: the width of the window itself. This gives you the base figure for all your later calculations.

1. Measure across the outside of the window frame, from outer edge to outer edge.
2. If there is decorative trim or architrave, include it in your measurement.
3. Record the width to the nearest half centimetre or quarter inch.

If your window is set within a deep recess, you still measure the frame on the face of the wall where your brackets will sit, not inside the recess (unless you are deliberately fitting the rod inside a niche, which is uncommon for double rods). For bay windows, measure each straight section separately, where each individual rod or track will be placed.

Repeat the measurement once or twice to be sure. If you find a small difference each time, use the largest number so you do not accidentally under-size your curtain rod.

Step 2: Add overhang on each side

The overhang is the extra length of rod that extends beyond the actual window frame. This space allows curtains to stack off the glass when open, maximises natural light and helps your window look more balanced on the wall. For double rods, both the inner and outer curtains generally share the same overhang.

As a starting point, many people use:

• 10–15 cm of overhang on each side for small to medium windows
• 15–20 cm (or more) on each side for wide windows or patio doors

You can fine-tune this based on your wall space and desired look:

• If you want the window to look wider, increase the overhang.
• If there are obstacles (e.g. a chimney breast or wardrobe), you may need to reduce one side slightly.

Now use the simple formula:

Rod length = Window width + Left overhang + Right overhang

For example, if your window frame is 120 cm wide and you choose 15 cm overhang on each side:

Rod length = 120 + 15 + 15 = 150 cm

This target length applies to both the inner and outer rods. When choosing an extendable set such as a black extendable double curtain pole, make sure your calculated length falls near the middle of its adjustable range, not right at the limit.

Step 3: Allow for brackets and finials

Now that you have a target rod length, you need to check how the brackets and finials (end caps or decorative ends) fit into that space. With double rods, a single wall bracket will usually support both the front and back rods, so their position is even more important.

Most double rods use one bracket at each end and, if the span is long, one or more centre brackets. The brackets are usually set a few centimetres in from the rod ends, leaving space for the finials. Manufacturers often specify a recommended maximum distance between brackets to avoid sagging.

When planning bracket placement:

• Check how wide the bracket base is and be sure it clears the edge of the window frame or trim.
• Make sure the finials will not hit walls, wardrobes or other obstacles when fully installed.
• For very wide spans, consider whether an extra support bracket will sit over the glass area and how it might affect curtain movement.

If you have already chosen a specific rod kit, such as an extra-long extendable double pole, it helps to look at its product diagram to see the minimum distance needed on each side for brackets and finials. Add a small safety margin in your planning so you have flexibility when marking holes.

Step 4: Decide on the mounting height for double rods

Mounting height has a big impact on how your windows and walls look. Hanging double curtains higher than the top of the frame tends to make the whole room feel taller and more finished, and it also gives enough space for the two rods and brackets.

A common guideline is to place the top of the bracket:

• 8–15 cm above the window frame or
• About one-third to halfway between the top of the frame and the ceiling or coving

For double rods, you also need to ensure:

• The rear rod (for sheers) hangs at a height that lets the fabric clear the frame and any handles.
• The front rod (for main curtains) sits slightly in front but level with the back rod so the curtain tops align neatly.

If you have floor-length curtains, measure from your intended rod height down to the floor. For a tailored look, subtract about 1–2 cm to keep the hems from dragging. For a more relaxed, pooled look, add a few extra centimetres. Make a note of this number on your worksheet, especially if you have not yet purchased your curtains.

Step 5: Check projection and clearance from the wall

Projection is how far the rods sit out from the wall. Double brackets are designed so the back rod is closer to the wall and the front rod is further out. This staggered design ensures the two layers of curtains do not clash or bunch up awkwardly.

Before finalising your measurements, check:

• The distance from wall to back rod – will sheer curtains clear any window handles, vents or existing blinds?
• The distance from wall to front rod – will main curtains hang straight without hitting radiators, deep sills or furniture?

If your window has very deep handles or a thick sill, you may need brackets with a slightly larger projection. Some extendable double rod sets include adjustable brackets for this reason, giving you more flexibility on tricky windows.

Measuring for different window types

Once you understand the basic steps, you can adapt them to almost any window. Here are some straightforward examples and formulas for common situations.

Standard windows (living rooms, bedrooms, kitchens)

Standard single windows are usually the easiest to measure. Use the base formula and then adjust the overhang to suit your wall space and the look you want.

Example: Window frame width = 100 cm. You choose 15 cm overhang on each side.

Rod length = 100 + 15 + 15 = 130 cm

Now check product ranges. An extendable double rod from around 76–222 cm gives you plenty of room to position the rod at roughly 130 cm within that range. If you pick something like a 76–222 cm double curtain pole, you can adjust it precisely to your measured length.

Tall or floor-length windows

For tall windows, the width calculation remains the same, but mounting height and curtain drop need extra thought. Because there is more visible wall, hanging the rods higher can be particularly flattering, drawing the eye upward and balancing the proportions.

Measure as follows:

1. Measure window width and add overhang as usual.
2. Decide on a mounting height that feels visually pleasing and leaves enough room for both rods and any crown moulding.
3. Measure the drop from that height to the floor to work out curtain length.

Double-check that both the inner and outer curtains will hang to the same point, unless you are deliberately choosing a shorter sheer layer. If you have a radiator beneath the window, you may prefer curtains that stop just below the sill to avoid blocking heat.

Sliding doors and patio doors

Sliding and patio doors usually need wider rods and sometimes heavier-duty hardware, as there is more glass to cover and typically more fabric involved. The principles remain the same, but the overhang becomes more important because you need space for the curtain stack.

For doors that you use frequently, it is often best to have the curtain stack mostly on the wall next to the opening, so the door can slide or swing freely. This can mean adding more overhang to one side than the other.

Example: Door opening width = 180 cm. You want most of the curtain to stack to the left.

• Left overhang: 30 cm
• Right overhang: 15 cm
• Rod length = 180 + 30 + 15 = 225 cm

Here you would choose an extendable double rod that comfortably covers around 225 cm, such as a long-range set running up to approximately 305 cm. A robust option like an extendable double pole suitable for 167–305 cm gives you enough strength and flexibility for wide spans.

Bay windows and angled spaces

Bay windows are more complex because each section of the bay may require its own rod segment, and the brackets may need to be angled or specially designed to follow the shape. For double rods, some people choose flexible tracks rather than rigid poles, but you can still apply the same basic measuring approach.

1. Measure each straight section of the bay separately along the line where the rod or track will sit.
2. Add modest overhangs to the outer sections, being careful not to run into the corners of the bay too aggressively.
3. Plan bracket positions on each section so they are evenly spaced and do not interfere with the angles.

Because bay windows vary widely, it is helpful to sketch the layout and note each individual measurement. If you are unsure, taking slightly more length and using adjustable or cut-to-size hardware can provide some flexibility during installation.

Tip: When measuring tricky bays or very wide spans, lightly mark bracket and finial positions on the wall with a pencil first. Step back, check the proportions visually, then confirm your final rod length based on what looks balanced as well as what fits mathematically.

Inner vs outer rod sizing and fabric fullness

In most double rod setups, both rods run the same overall width. However, the amount of fabric on each rod can differ. Sheer curtains often use more width relative to the rod to create a soft, gathered look, while blackout or heavier curtains may use slightly less fullness.

A common guide for fabric fullness is:

• Sheers: 2–3 times the rod width
• Medium-weight curtains: 1.5–2 times the rod width
• Blackout or heavy curtains: around 1.5–2 times the rod width depending on taste

For example, if your rod length is 180 cm:

• Sheers could total 360–540 cm of fabric width across all panels.
• Main curtains could total 270–360 cm of fabric width.

When buying ready-made curtains, look at the total width of both panels combined and compare it to your measured rod length. This helps ensure you have enough fabric for a full, attractive gather on both the inner and outer rods.

Simple formulas you can reuse (worksheet style)

You can convert the measuring process into a small set of reusable formulas. Write these at the top of your printable worksheet or in your notes:

• Rod length (both rods) = Window width + Left overhang + Right overhang
• Mounting height = Frame top + Chosen distance above frame (or chosen point between frame and ceiling)
• Curtain length (drop) = Rod height to floor (or sill) ± desired clearance
• Total curtain fabric width = Rod length × Fullness factor (e.g. 2 or 2.5)

Create separate lines for each window in your home and fill these in as you measure. When it is time to choose double rod sets and curtains, you will have all the key numbers ready to compare with product descriptions.

Conclusion

Measuring windows for double curtain rods is essentially a series of small, logical steps: capture the true window width, decide how much overhang you want, calculate your rod length using a simple formula and then choose a mounting height that flatters the room while leaving enough space for both rods. Once you have those numbers written down, choosing compatible double rod sets and curtains becomes much easier.

Whether you are dressing a compact bedroom window or spanning a large patio door, the same principles apply. Look for strong, adjustable double rod sets that comfortably cover your measured span, such as a 22 mm nickel extendable double pole for medium windows or a long-range extendable double pole for wider openings. With careful measuring and a few consistent formulas, you can create layered window treatments that both look good and work smoothly day after day.