What Is a Window Blind?
A window blind is a type of window covering made of vertical or horizontal slats of a hard material such as wood, plastic, or metal. A control cord or wand at the side lets you open or close the slats to regulate light and privacy.
Inside Mount vs. Outside Mount
- Inside mount — the blind sits within the window frame for a clean, built-in look. Use the smallest width measurement so the blind fits without binding.
- Outside mount — the blind extends beyond the frame, making the window appear larger and blocking more light. Add 1.5 in (3.8 cm) of overlap on each side and 1.5 in (3.8 cm) at the top.
How to Measure Your Window for Blinds
- Measure the width at the top, middle, and bottom of the window frame from the inside edge.
- Measure the height at the left, center, and right of the window frame from the inside edge.
- Record all six measurements.
How Our Blind Size Calculator Works
- Choose your mount type (inside or outside) and unit system (American inches or metric cm).
- Enter all three width measurements (top, middle, bottom) and all three height measurements (left, center, right).
- For an inside mount, tick the sill clearance box to subtract ¼ in (6 mm) so the blind does not drag on the sill.
- Optionally enter the price of one blind to get an instant cost estimate in your preferred currency.
- Click Calculate and the recommended blind width and height appear instantly.
How to Manually Calculate Blind Size
Inside Mount
- Width = smallest of top / middle / bottom measurements.
- Height = largest of left / center / right measurements (subtract ¼ in / 6 mm if you want clearance from the sill).
Outside Mount
- Width = largest of top / middle / bottom + 3 in (7.6 cm) — 1.5 in (3.8 cm) overlap on each side.
- Height = largest of left / center / right + 1.5 in (3.8 cm) — overlap above the frame.
Standard Blind Sizes Available in Stores
There are no universal standard blind sizes. Most retailers cut blinds to suit the three most common window types:
- Picture windows — 12–96 in (30–244 cm) high, 24–96 in (61–244 cm) wide.
- Slider windows — 24–60 in (61–152 cm) tall, 36–84 in (91–213 cm) wide.
- Double hung windows — 36–72 in (91–183 cm) high, 36–84 in (91–213 cm) wide.
If your windows fall outside these ranges, you can have blinds cut to size at the store or order custom-made blinds.
Frequently Asked Questions
Can I cut blinds to fit my window?
Many horizontal vinyl and aluminum blinds can be trimmed to width with a hacksaw or blind-cutting tool. Always check the manufacturer's instructions before cutting, and keep cuts to a minimum to avoid damaging the slats.
What if I measure wrong?
For inside mounts, too wide is worse than too narrow — a blind that is even slightly too wide will not fit inside the frame. For outside mounts, a few extra inches are usually fine because the blind covers the wall around the frame anyway.
Do I need a professional to install blinds?
Most blinds come with simple hardware and instructions for a DIY installation. You will need a drill, a level, a tape measure, and the screws provided. If your walls are plaster or tile, you may need masonry anchors.
How do I choose between inside and outside mount?
- Choose inside mount if you want a clean look and have at least 1½ in (3.8 cm) of depth inside the frame.
- Choose outside mount if your windows are shallow, oddly shaped, or you want to maximise light blockage and make the window appear larger.