Window Blind & Curtain Size Calculator

Window Blinds and Curtains Guide

Inside vs Outside Mount

Inside mount (within recess): the blind fits inside the window frame, giving a clean, built-in look. Measure the exact width of the recess at the top, middle, and bottom — use the narrowest measurement, then deduct 10mm for operation clearance. Measure the drop from the top of the recess to the sill. The blind manufacturer will usually make a small deduction from width automatically. Outside mount (on wall or above frame): provides better light blocking (covers the frame edges), can make small w

Curtain Measurements

Track or pole position: typically 150mm above the frame (to give the illusion of height) and 200-300mm beyond the frame on each side (so curtains stack off the glass when open). Pole width = window width + 400-600mm (200-300mm each side). Curtain width: total fabric needed = pole/track width × fullness factor (1.5-3, depending on heading type). Each curtain panel = total fabric width ÷ 2. Drop: sill length = from eyelet/hook to sill minus 5-10mm. Floor length = from eyelet/hook to floor minus 15

Blackout and Thermal Properties

True blackout blinds require the fabric to be bonded with a blackout coating and the blind to be fitted with side channels or close to the wall to eliminate light gaps around the edges. A standard 'blackout' roller blind without side channels will allow light in around the sides — most effective for darkening a room at night, less effective for shift workers or babies in summer. Thermal properties: cellular (honeycomb) blinds trap air and provide genuine insulation improvement — measured by the

Child Safety Requirements

Since 2014, UK regulations require all new blinds to be supplied with cord safety devices or be cordless to prevent strangulation risk to children. The Child Safety Regulations apply to all blinds with accessible cords — including Roman, Venetian, and vertical blinds. Looped cords must be fitted with a safety device that breaks the loop under tension. When buying second-hand or non-UK blinds, check cord safety as a priority. Cordless roller and cellular blinds are the safest option and now commo