Window Blinds Size Calculator
Calculate the correct blinds width and height for any window.
Covers inside and outside mount types with deduction and add-on measurements for each style.
Recommended Blinds Size
Window blind sizing combines two separate calculations: the correct dimensions for a perfect fit, and the total material cost at your chosen price-per-square-foot.
Width formula:
- Inside mount: Measure the inside of the window frame at three points (top, middle, bottom). Use the narrowest measurement. Deduct 0.25–0.5 inches so the blind slides freely without binding.
- Outside mount: Add 1.5–3 inches to each side of the frame. A 3-inch total overlap (1.5 per side) blocks light leakage; 6 inches total (3 per side) gives a more dramatic, room-darkening effect.
Height formula:
- Inside mount: Measure from the top of the sill to the top of the frame. Use the tallest measurement.
- Outside mount: Add 3–4 inches above the frame to conceal the headrail, and add the sill overlap you prefer (0–3 inches below the sill).
Cost formula: Total Cost = (Width × Height in sq ft) × Price per sq ft
Where:
- Width and Height are in feet (divide inches by 12)
- Price per sq ft — standard roller blinds run $1–$4/sq ft; cellular shades $3–$8/sq ft; motorized shades $8–$20/sq ft
What each variable means:
- Inside vs outside mount — inside mounts look clean and architectural; outside mounts suit windows with shallow depth or make small windows appear larger
- Deduction allowance — prevents the blind from jamming against the frame when raised or lowered; 0.25 inches per side is standard
- Light gap — outside mounts with wider overlap significantly reduce side-light leakage, critical for blackout applications
Reference: standard blind prices by type
- Roller blinds: $15–$80 per blind
- Venetian blinds (aluminum): $20–$100 per blind
- Wood blinds: $40–$200 per blind
- Cellular/honeycomb shades: $50–$250 per blind
- Motorized shades: $150–$600+ per blind
Worked example: You have a window 36 inches wide × 48 inches tall. You want an inside mount roller blind at $2.50/sq ft.
- Deducted width = 36 − 0.375 (3/8 inch deduction) = 35.625 inches
- Height = 48 inches (no deduction needed)
- Area = (35.625 ÷ 12) × (48 ÷ 12) = 2.97 × 4.0 = 11.88 sq ft
- Cost = 11.88 × $2.50 = $29.70
For a set of five identical windows, total cost = $148.50 before installation.