How to measure your custom curtains: the complete guide for every window type
To measure a custom curtain, you need two dimensions: the width (measured from the rod or frame, plus 30 to 40 cm of lateral overhang) and the height (from the rod to the floor, plus 2 to 5 cm for the drop). For a technical curtain (thermal, blackout, soundproof), the margins are larger: 15 to 20 cm of overhang on each side, and almost direct contact with the floor.
The measurement method changes depending on the window type. This guide covers each configuration: classic window, bay window, entrance door, attic window. The goal is to order with the correct dimensions on the first try.
Why measurements are more important than fabric
A poorly sized curtain loses its performance, regardless of its fabric. Thermal and acoustic performance tests show that a curtain that is too narrow (without a lateral overhang of 15-20 cm) loses 30 to 40% of its insulation effectiveness. A curtain that is too short (5 cm above the floor) loses 20 to 30% of its ability to block cold and noise due to floor draft effect.
According to ADEME, windows account for 10 to 15% of a home's heat loss, which explains why a poorly sized curtain cancels out part of the expected gain.In concrete terms: a high-performance thermal curtain (7 °C gain measured*) installed without lateral overhang will only deliver 4 to 5 °C of actual gain. A 100% blackout curtain that is 5 cm too short will allow enough light to filter through to disturb sleep (5 to 10 lux). Measurement errors are the primary cause of disappointment after purchasing a custom curtain.
Summary table: how to measure according to your window
| Window type | Width | Height | Lateral overhang | Drop to floor |
|---|---|---|---|---|
| Classic window (existing rod) | Rod x 1.5 to 2 (fullness coefficient) | Rod to floor + 2 to 5 cm | Already included in the rod | Skims the floor (2-3 cm gap) |
| Window without rod | Outer frame + 30 to 40 cm | Rod placement to floor + 2 to 5 cm | 15 to 20 cm on each side | Skims the floor (2-3 cm gap) |
| Bay window | 3 measurements (top/middle/bottom), keep the largest + 30-40 cm | 3 measurements (left/center/right), keep the largest | 15 to 20 cm on each side | Skims the floor |
| Entrance door | Outer frame + 40 to 60 cm | Rod to floor (full contact) | 20 to 30 cm on each side | Floor contact (1-2 cm excess) |
| Attic window | Total straight-line width | Maximum slope height | Varies by configuration | Depends on installation |
Universal rule: for technical curtains (thermal, blackout, soundproof), always take the largest measurement and round up to the nearest centimeter. A slightly too large curtain is easy to manage (hem, floor drop), a too small curtain cannot be fixed.
Classic window with existing rod
This is the most common case. You already have a rod installed above your window.
For the width: measure the rod from end cap to end cap (not the window, not the wall). For a pleated look (most common and most thermally efficient), multiply by 1.5 to 2. Example: a 120 cm rod results in a curtain 180 to 240 cm wide. If you order two panels, divide by two: 90 to 120 cm per panel.
For the height: measure from the top of the rod (or the ring, depending on the type of attachment) to the floor. Add 2 to 5 cm for a drop that skims the floor. A curtain that stops 10 cm from the floor loses elegance and insulating performance (cold air draft from below).
For detailed measurement method adapted to Kurtens curtains (with automatic price calculation), consult our interactive size guide.
Window without rod: how to measure from scratch
No rod, no support. You must first decide where the rod will be positioned.
Rod position: 10 to 15 cm above the top of the window. The higher the rod, the more the curtain gives an impression of height to the room. For maximum effect, some install the rod just below the ceiling.
Width: measure the outer width of the window frame (not the glass, the entire frame). Add 30 to 40 cm (15 to 20 cm on each side). Without this lateral margin, air circulates on the sides and thermal, acoustic, and blackout performance drops by 30 to 40%.
Height: measure from the planned rod location to the floor. Add 2 to 5 cm for the drop. If you choose eyelets, the top of the curtain extends approximately 2 to 3 cm above the rod: take this into account in your measurement.
Bay window: pitfalls to avoid
Bay windows are the most delicate surfaces to measure: often very wide (200 to 400 cm), sometimes asymmetrical, with walls that are not always perfectly parallel.
Essential rule: measure in three places. Width at the top, middle, and bottom. Height on the left, center, and right. Take the largest measurement in each direction. Discrepancies can be 1 to 3 cm, enough to create a visible gap if you take the wrong measurement.
For a bay over 200 cm, two panels that meet in the center are preferable to a single massive curtain. Each panel should overlap by 10 to 15 cm in the center when closed. Without this overlap, light, cold, and noise will pass through the middle.
At Kurtens, the maximum height for online orders is 270 cm, which covers the vast majority of residential bay windows. For any larger measurement, contact our team for a quote.
Entrance door: measuring for insulation
A curtain in front of an entrance door is one of the most effective solutions to cut down drafts. The measurement is different from a window because you need to consider the door opening and larger insulation margins.
Width: outer door frame + 40 to 60 cm (20 to 30 cm on each side). The curtain must significantly extend beyond the frame to block lateral air infiltration. A curtain that stops exactly at the frame is almost useless for insulation.
Height: from the rod to the floor, with floor contact (1-2 cm excess). The space under the door is the main leakage point (up to 45 cm2 of opening on a standard 90 cm door with a 5 mm gap).
Rod projection: 10 to 15 cm from the wall so that the curtain does not obstruct the opening. Consult our article on what 30 dB attenuation means if your door has both thermal and sound problems.
Attic windows and atypical configurations
Roof windows (Velux type) and sloping windows pose a particular challenge. A classic curtain cannot hang in front of an inclined window without moving away from the glazing.
Two solutions exist:
- Direct installation on the frame: blind or curtain with a lateral guiding system holding the fabric against the glass. Measure the width and height of the inner frame of the roof window.
- Rod at the base of the slope: placed where the wall meets the sloped ceiling, the curtain hangs vertically and covers the entire sloped surface. Measure the wall width and the height from the floor to the wall/ceiling junction point.
For arched, corner, or curved bay windows: measure the total width in a straight line (not following the curve) and the maximum height. The curtain will hang straight in front of the glazed surface. For any atypical configuration, contact our team with your measurements and a photo.
The 5 most common measurement errors
- Error 1: measuring the window instead of the rod. The width of the curtain should match the rod, not the glass. The rod always extends 15 to 20 cm beyond the window on each side.
- Error 2: forgetting the fullness coefficient. A flat curtain without pleats loses aesthetic appeal and insulating performance (no air pocket between the folds). Multiply the rod width by 1.5 to 2.
- Error 3: measuring from the ceiling instead of the rod. The curtain starts at the rod, not the ceiling. If the rod is 10 cm from the ceiling, these 10 cm are not part of the curtain height.
- Error 4: ignoring the type of attachment. An eyelet curtain extends 2 to 3 cm above the rod. A pencil pleat curtain starts directly below the hooks. The visible height varies. Consult our attachment guide.
- Error 5: taking only one measurement. Walls are not always square, and floors are not always level. Measure the height on the left and right, and the width at the top and bottom. Always take the largest measurement. Common deviation: 1 to 3 cm.
Standard size or custom-made: how to decide
| Criterion | Standard size | Custom-made |
|---|---|---|
| Dimensions | 4 sizes: 100x150, 150x230, 250x230, 300x270 cm | To the nearest centimeter, up to 270 cm height, free width |
| When to choose | Window with common dimensions, acceptable tolerance | Atypical dimensions, maximum technical performance, precise aesthetics |
| Technical performance | Good if size matches | Maximum (full coverage, zero leakage) |
| Lead time | Immediate shipping | Manufacturing 2 to 3 weeks |
| Price | More affordable | Slightly higher (fabric to exact dimensions) |
Custom-made is recommended whenever technical performance matters: total blackout and thermal insulation directly depend on full window coverage. If no standard size matches, the Kurtens customizer allows you to enter your exact dimensions and see the price instantly.
*Data from tests conducted under optimal conditions.
Frequently Asked Questions
Should the curtain touch the floor?
Ideally, yes. A curtain that skims the floor (2 to 3 cm gap) is more elegant and performs better. A gap of 5 cm or more at the bottom lets in cold, light, and noise due to drafts. For a technical curtain (thermal, blackout, soundproof), floor contact or minimal gap is recommended. A purely decorative curtain can tolerate a 1 to 2 cm gap.
What curtain width for a 120 cm window?
If your rod is 120 cm, your curtain should measure between 180 and 240 cm wide (120 x 1.5 to 2, fullness coefficient). This coefficient creates the pleats that give the curtain its natural drape and improve its insulating performance (air pocket between the folds). With two panels: 90 to 120 cm per panel, with 10 to 15 cm of central overlap.
How to measure a curtain for a bay window?
Measure width and height in three different places (walls and floor are not always perfectly level, common deviation of 1 to 3 cm). Take the largest measurement in each direction. Add 30 to 40 cm of lateral overhang. For bays over 200 cm, two panels with 10 to 15 cm of central overlap provide a better look and easier handling.
What if I make a mistake in my measurements?
Measure twice before ordering. If an error still occurs, Kurtens offers the Exact-Fit Guarantee (29.90 euros): if your measurements are incorrect, the curtain is re-manufactured to the correct dimensions at no extra cost. This provides security and eliminates the stress of taking measurements, especially useful for windows with atypical dimensions.
Do measurements change depending on the type of curtain?
The measurement method is the same, but the recommended margins are larger for technical curtains. A decorative curtain can tolerate a few centimeters of lateral play. A blackout, thermal, or soundproof curtain must fully cover the window with an overhang of 15 to 20 cm on each side and a floor drop to block light, cold, and noise. The estimated performance loss without lateral overhang is 30 to 40%.
What fullness coefficient to choose for a custom curtain?
The fullness coefficient (or pleating coefficient) determines the extent of the curtain's pleats. Coefficient 1.5: light pleats, modern and clean look. Coefficient 2: marked pleats, classic and voluminous look. For technical curtains, a minimum coefficient of 1.5 is recommended because the pleats create air pockets that enhance thermal and acoustic insulation. A flat curtain (coefficient 1) loses aesthetic appeal and performance.
How to measure a curtain for an entrance door?
An entrance door requires larger margins than a window. Width: outer frame + 40 to 60 cm (20-30 cm on each side). Height: from the rod to the floor, with 1-2 cm excess (floor contact is essential to block infiltrations). Rod projection: 10-15 cm from the wall so as not to obstruct the door opening. Lateral overhang is crucial because the space under and around the door is the primary point of thermal leakage in a home.
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