Curtain Size Calculator

Window Measurements

Taking accurate window measurements is the first step to perfectly sized curtains:

• Window width: For inside mount, measure the exact width of the window opening inside the casing. For outside mount, measure the width of the window frame.
• Window height: For inside mount, measure the exact height of the window opening. For outside mount, measure from where you'll place the rod to where you want the curtains to end.
• Use a metal tape measure: Cloth measuring tapes can stretch and give inaccurate measurements.
• Measure twice: Double-check all measurements to avoid costly mistakes.

Rod Measurements

Your curtain rod placement affects both function and appearance:

• Rod width: For outside mount, the rod should extend 8-12 inches beyond each side of the window frame (16-24 inches total). This allows curtains to stack off the window when open, maximizing light.
• Rod height: For outside mount, position the rod 4-6 inches above the window frame to create the illusion of height. In rooms with low ceilings, you can mount them even higher, up to ceiling level.
• Rod diameter: Consider the weight of your curtains when selecting rod diameter. Heavier curtains require thicker rods (1-2 inches) for proper support.

Additional Measurements

Don't forget these important measurements for complete curtains:

• Hem allowance: Typically 4-8 inches for a double-folded hem that gives weight and structure to the bottom of the curtain.
• Header allowance: The fabric above the rod pocket or other hanging mechanism, typically 2-3 inches, which creates a decorative finish at the top.
• Fullness factor: Multiply your window or rod width by 1.5-3 to determine the total curtain width needed for proper fullness and draping.

Inside Mount Curtains

Inside mount curtains are installed within the window frame or casing.

Advantages:

• Create a clean, built-in look
• Showcase decorative window molding or trim
• Work well in deep window casings
• Take up less wall space
• Ideal for windows with window seats or furniture placed directly beneath

Disadvantages:

• Provide less light blockage (gaps at edges)
• Limit curtain fullness due to space constraints
• Require precise measurements
• Not suitable for shallow window casings
• May not accommodate thicker curtain rods

Measuring for Inside Mount:

• Measure the exact width and height of the window opening inside the casing
• Subtract 1/4 inch from width measurements for clearance
• Choose tension rods or specialized inside mount hardware

Outside Mount Curtains

Outside mount curtains are installed on the wall surrounding the window.

Advantages:

• Make windows appear larger
• Provide better light control and privacy
• Allow for greater curtain fullness
• Hide unattractive window frames
• Work with any window, regardless of casing depth
• Can create the illusion of higher ceilings

Disadvantages:

• Cover decorative window molding
• Take up more wall space
• Require more fabric
• May interfere with wall decorations or furniture placement

Measuring for Outside Mount:

• Measure the width of the window frame and add 8-12 inches on each side
• Measure from where the rod will be placed to where you want curtains to end
• Account for rod height (typically 4-6 inches above window)
• Consider wall space and obstacles like radiators or furniture

Choosing the Right Mount

Consider these factors when deciding between inside and outside mount:

• Window features: If you have beautiful molding you want to showcase, inside mount may be preferable. For plain or unattractive frames, outside mount can hide them.
• Light control needs: If complete darkness is desired (for bedrooms), outside mount provides better light blockage.
• Window depth: Inside mount requires at least 2-3 inches of depth in the window casing.
• Room aesthetics: Consider your overall design scheme and how the curtains will complement other elements in the room.

Sill Length

Sill-length curtains end at or just above the window sill.

• Typical length: Varies based on window size, typically 24-45 inches
• Best for: Kitchen windows, bathroom windows, windows above furniture or radiators
• Style: Casual, practical, traditional
• Measuring tip: Measure from the rod to the window sill and subtract 1/2 inch for clearance

Below Sill

Below-sill curtains extend 4-6 inches below the window sill.

• Typical length: Window sill length plus 4-6 inches
• Best for: Windows with radiators or furniture positioned below but not directly against the wall
• Style: Transitional, slightly more formal than sill length
• Measuring tip: Measure from the rod to 4-6 inches below the sill

Floor Length

Floor-length curtains stop just above the floor, creating a clean, tailored look.

• Typical length: 84-108 inches, depending on ceiling height
• Best for: Living rooms, dining rooms, bedrooms, any room where a polished look is desired
• Style: Versatile, works with most decorating styles
• Measuring tip: Measure from the rod to 1/2 inch above the floor
• Professional look: This is the most universally flattering curtain length

Puddle

Puddle-length curtains extend onto the floor, creating a luxurious, romantic effect.

• Typical length: Floor length plus 1-6 inches (or more for dramatic effect)
• Best for: Formal living rooms, master bedrooms, rarely opened curtains
• Style: Elegant, dramatic, romantic, traditional
• Measuring tip: Measure from the rod to the floor, then add 1-6 inches for desired puddle effect
• Maintenance note: Not practical for high-traffic areas or homes with pets, as they collect dust and can be tripping hazards

Choosing the Right Length

Consider these factors when selecting your curtain length:

• Room function: High-traffic areas benefit from sill or floor-length curtains that won't be stepped on.
• Furniture placement: If you have furniture against the wall under windows, sill or below-sill lengths prevent fabric bunching.
• Cleaning considerations: Puddle-length curtains require more frequent cleaning as they collect dust and pet hair.
• Visual effect: Longer curtains create the illusion of height, while shorter curtains can make a room feel more casual.
• Air circulation: Consider radiators or air vents that might be blocked by longer curtains.

Height Placement

The height of your curtain rod dramatically affects the appearance of your windows and room:

• Standard placement: 4-6 inches above the window frame creates a classic look and makes windows appear taller.
• High placement: Mounting rods close to the ceiling (8-12 inches above the window or halfway to the ceiling) maximizes the height illusion and works well in rooms with low ceilings.
• Ceiling mount: Rods can be mounted directly to the ceiling in rooms with very low ceilings or to create a dramatic floor-to-ceiling effect.
• Inside casing: For inside mount curtains, the rod is placed within the window casing, typically at the top.

Width Placement

Proper rod width ensures curtains function well and enhance your windows:

• Standard extension: Extend the rod 8-12 inches beyond each side of the window frame. This allows curtains to stack mostly off the window when open, maximizing light and making the window appear wider.
• Minimal extension: In tight spaces with limited wall area, a 3-4 inch extension on each side is the minimum recommended to allow curtains to clear the window when open.
• Wall-to-wall: For a dramatic effect or to disguise awkward windows, rods can span an entire wall.
• Inside casing: For inside mount, the rod should be 1/4 inch narrower than the inside measurement of the window casing.

Rod Types and Support

Choose the right rod type and ensure proper support:

• Rod diameter: Match rod thickness to curtain weight. Lightweight curtains: 3/4-1 inch diameter; Medium-weight: 1-1.5 inch; Heavy curtains: 1.5-2 inch or double rods.
• Support brackets: Install brackets at each end and in the middle for rods longer than 48 inches. For heavy curtains or rods over 96 inches, add brackets every 24-30 inches.
• Tension rods: Suitable only for lightweight curtains in inside mount applications, typically up to 36 inches wide.
• Secure mounting: Use appropriate anchors and screws based on your wall type (drywall, plaster, concrete). Whenever possible, mount into wall studs for maximum support.

Special Considerations

Address these common rod placement challenges:

• Corner windows: Use a corner connector to join rods at a 90-degree angle, or mount separate rods that meet at the corner.
• Bay windows: Use flexible or hinged rods that can follow the angle of bay windows, or mount separate rods for each section.
• Arched windows: Mount the rod above the arch to create a clean line, or use specialty curved rods to follow the arch shape.
• French doors: Mount rods directly to the door frame using door-mounted brackets, positioning them high enough to clear door handles.
• Sliding glass doors: Use extra-long, sturdy rods mounted 4-6 inches above and extending 12-15 inches beyond each side of the door frame.

Calculating Fabric Width

Determining the right amount of fabric width ensures proper fullness:

• Fullness factor: Multiply your window or rod width by the desired fullness factor:
  • Light fullness (1.5×): Tailored, contemporary look
  • Standard fullness (2×): Classic, versatile appearance
  • Full appearance (2.5×): Rich, luxurious look
  • Extra full (3×): Dramatic, opulent style
• Panel calculation: Divide the total curtain width (rod width × fullness) by the usable fabric width (typically fabric width minus 1 inch for seam allowances).
• Example: For a 60-inch rod with 2× fullness using 54-inch wide fabric:
  • Total curtain width: 60 × 2 = 120 inches
  • Usable fabric width: 54 - 1 = 53 inches
  • Panels needed: 120 ÷ 53 = 2.26, rounded up to 3 panels

Calculating Fabric Length

Determine the fabric length needed for each panel:

• Basic length: Measure from the rod to the desired endpoint (sill, below sill, floor, or puddle).
• Add allowances: Add hem allowance (typically 4-8 inches) and header allowance (typically 2-3 inches).
• Pattern matching: For patterned fabrics, add extra length for pattern matching (typically 4-12 inches depending on pattern repeat).
• Example: For 84-inch floor-length curtains with 6-inch hem and 3-inch header:
  • Total length per panel: 84 + 6 + 3 = 93 inches

Total Fabric Calculation

Calculate the total fabric yardage needed:

• Multiply: Number of panels × length per panel = total fabric length
• Convert to yardage: Divide total length by 36 to get yards (or by 100 for meters)
• Add extra: Add 10% for mistakes and adjustments
• Example: For 3 panels at 93 inches each:
  • Total fabric length: 3 × 93 = 279 inches
  • Yardage: 279 ÷ 36 = 7.75 yards
  • With 10% extra: 7.75 × 1.1 = 8.53 yards, rounded up to 8.75 yards

Lining Considerations

Factor in lining requirements for better draping, light control, and insulation:

• Standard lining: Calculate the same amount as your main fabric, though you can reduce fullness to 1.5× for lining.
• Blackout lining: Same as standard lining but may be slightly narrower than the main fabric.
• Interlining: For thermal or sound insulation, calculate the same as standard lining.
• Tip: Lining fabric is typically 54 inches wide, similar to drapery fabric.