Window Size and Sill Height Standards

Windows are usually drawn by the architect or builder long before anyone decides where the bed, sofa, desk or kitchen counter will go, and yet they control almost every one of those decisions. A sill that is too low puts glass behind the sofa and a radiator of afternoon heat at the back of every seated head. A kitchen window that starts at 900 mm collides with a counter at 850–900 mm. A bedroom window placed where the headboard must go forces the bed onto the wrong wall. Once the brickwork and lintels are built, these choices are almost impossible to change.

Indian practice has settled on a small set of window heights and sizes that work for most rooms: a sill at 900 mm, a head at the 2100 mm lintel line shared with doors, and widths in steps of about 300 mm. The standard article on door and window sizes on this site lists those headline numbers. This article goes deeper into the window itself — why each sill height exists, how the building code's ventilation guidance translates into window sizes, how head height decides how far daylight reaches into a room, and what changes for kitchens, bathrooms, studies, staircases and high-rise flats.

All numbers are given in millimetres with feet-and-inches equivalents where useful. Building-code figures are presented as guidance as they are commonly cited from the National Building Code of India 2016 and local bye-laws, which vary by city; the local development control regulations always govern an actual approval.

Where window sizes come from

Traditional Indian houses used openings very differently from modern flats. Havelis and pol houses of Gujarat and Rajasthan had small, often high windows on the street side, timber shutters rather than glass, and jharokhas and jaalis that let people sit low and look out unseen. Light and air came largely from internal courtyards. Rooms were used at floor level, so many openings had low sills suited to people sitting on the floor.

Colonial bungalows introduced tall timber windows with fanlights and louvred shutters, often reaching close to ceilings of four metres or more, which carried hot air out high in the room. After independence, public works departments and municipal bye-laws standardised smaller openings in reinforced-concrete frame buildings: steel windows on a 900 mm sill under a continuous lintel and chhajja at door-head height became the pattern of government housing and early apartments across India. That pattern — sill at 900 mm, head at about 2100 mm, chhajja above — is still the default in most Indian flats, now built with aluminium or UPVC frames instead of steel and timber.

What the building code asks for

The guidance most often quoted from the National Building Code of India 2016 — in the general building requirements of Part 3 and in the lighting and ventilation section of Part 8 — is that habitable rooms and kitchens should have openings, excluding doors, with an aggregate area of at least one-tenth of the floor area, opening onto an external open space or a permitted shaft. Another commonly cited clause is that no part of a room should be counted as lit by a window if it is more than about 7.5 m away from it. Bathrooms and WCs have their own minimum opening or may use mechanical exhaust instead, as explained in the bathroom size guide on this site. Local development control regulations repeat or modify these figures, and some ask for more.

Two points are often misunderstood. First, one-tenth is a minimum for approval, not a design target. A room that just meets it will usually feel dim towards the back, especially on lower floors in dense Indian neighbourhoods where buildings shade each other. Many designers aim for glazing of roughly 15–20 per cent of the floor area in living rooms and bedrooms as practice guidance, balanced against heat gain on west and south faces. Second, a window that does not open does not ventilate. A two-track sliding window opens only about half its area at a time, while a casement opens nearly all of it, so when ventilation is the priority, the openable area should be checked against the one-tenth figure as well.

Standard window sizes

Because Indian floors are built with lintels at about 2100 mm, most window sizes are combinations of a fixed height — usually 1200 mm on a 900 mm sill — and a width chosen in steps of about 300 mm, matching the four-, five- and six-foot sizes that fabricators and masons are used to. Wider openings are split into more shutters or tracks. The table lists the common sizes and where each is used.

Fig. 1 shows why the 900 mm sill and 2100 mm head have survived. The window and the door share one lintel line, so a single lintel band and chhajja can run along the facade, and every opening in the room has the same head height. With the window 1200 mm tall, its sill at 900 mm sits just above the back of a typical sofa and above a 750 mm table or desk, so furniture can stand against the window wall without blocking the glass. In flats with a floor-to-slab height of 2850–3000 mm, there is 750–900 mm of wall above the lintel, which is where curtain pelmets, cove ceilings and split air-conditioners are usually placed.

Sill heights, room by room

The 900 mm sill is a good default, not a universal rule. Each room has furniture or fixtures that want the window at a particular height, and the sill should be chosen from them. The table and Fig. 2 give the common choices.

In the kitchen, the sill must clear the counter and leave room for a backsplash, so 1050 mm is the practical minimum over an 850–900 mm counter, and 1200 mm is more comfortable where the hob or sink sits below the window and a tap or splash guard is needed. In bathrooms, the ventilator is placed high — about 1800 mm or more — so it exhausts warm, moist air and screens the WC from outside; its head must stay below the bathroom's false ceiling, which commonly sits at 2200–2400 mm, so ventilators there are often 300–450 mm tall rather than 600 mm. In children's rooms and on upper floors, any sill below about 900 mm needs a guard or a restrictor, as described in the safety section below.

Head height and daylight depth

Sill height decides what fits below the window; head height decides how far daylight reaches into the room. A commonly cited rule of thumb in daylighting practice is that useful daylight from a side window reaches roughly 1.5 to 2 times the window head height into the room. With a head at 2100 mm, that is about 3.2–4.2 m — enough for a standard bedroom but not for the back of a deep living room. Raising the head to 2400 mm or more, which is possible where the lintel can be raised or where there is no chhajja below the slab, pushes good light deeper and makes rooms feel taller.

The chhajja above a window is the other half of the story. A projection of about 600–750 mm over a 1200 mm tall window keeps the high summer sun off the glass on south faces, while letting low winter sun in. On east and west faces, where the sun is low in the morning and afternoon, a horizontal chhajja alone does little; vertical fins, deep reveals, jaalis or external blinds are needed. Many modern flats drop the chhajja altogether for a clean facade, then compensate with tinted glass that darkens the room all day. A shaded clear glass almost always gives a better room than an unshaded dark one.

A worked example: sizing a bedroom window

Fig. 4 shows the full process for a 3000 × 3600 mm bedroom on the west side of a flat. The floor area is 10.8 m², so the one-tenth guidance asks for at least 1.08 m² of openings. A 1500 × 1200 mm window gives 1.80 m² of glazing, comfortably above the minimum and close to the 15–20 per cent practice target. As a two-track slider it opens about 0.9 m² at a time, so a small second opening on the adjacent wall — or a casement instead of a slider — helps ventilation. The window sits on the shorter wall away from the bed's headboard, on a 900 mm sill so that a study table can stand below it, and its west exposure calls for external shading or a deep reveal.

Safety: low sills, high-rise flats and children

A low sill is beautiful and dangerous in equal measure. In high-rise flats, any window whose sill is below about 900 mm, and any full-height glazing that opens, should be treated like a balcony edge. The options are a fixed guard rail at 1000–1100 mm — the same height recommended for balcony railings on this site — a fixed lower pane of toughened or laminated safety glass with only the upper part openable, or restrictors that limit the opening to about 100 mm. Children's rooms need restrictors whatever the sill height, and in a child's room on an upper floor, furniture that can be climbed — beds, desks, toy chests — should not stand directly under an openable window.

Glass near the floor also needs care. Large panes within reach of people walking — in full-height windows, French doors and low-sill windows — should be toughened or laminated safety glass so that an accidental impact does not produce large sharp shards. Grills, if used, should allow an escape route in an emergency; a fully fixed grill on every bedroom window can trap occupants in a fire, so at least one openable grill section with an internal lock is good practice.

Planning windows with the interior in mind

Interior designers can rarely move windows in a flat, but they can still plan around them well. Curtain pelmets need 150–250 mm of wall above the window head and 100–150 mm beyond each side so that open curtains do not cover the glass. Split air-conditioners need about 750 mm above the lintel line in a 2850 mm room, or they end up partly over the window. Window seats work best on low sills of 450 mm or with a built-up platform under a 900 mm sill. Blinds recessed into a window reveal need a reveal at least as deep as the blind's headrail. And where a builder offers a choice during construction, a slightly wider window on a 900 mm sill is usually worth more than a lower sill.

Where window standards are going

Window design in India is moving from minimum size towards performance. The Energy Conservation Building Code for commercial buildings and the Eco-Niwas Samhita for homes address how much glazing a building has, how well it is shaded and how much of it can be opened, because unshaded glass is one of the main sources of heat gain in Indian buildings. Better glass — low-emissivity and double glazing — is becoming more common in premium flats. At the same time, rising summer heat is bringing back old ideas: deep reveals, external shading, louvres and jaalis, and windows placed for cross-ventilation rather than for facade symmetry. The likely future is not bigger windows everywhere, but windows sized, shaded and placed for each orientation and each room.

Rules for window size and sill height

• Treat one-tenth of floor area as the minimum opening, not the target; aim for about 15–20 per cent glazing in main rooms where heat gain is controlled.
• Check the openable area too: a two-track slider opens only about half its size.
• Keep window and door heads on one line, typically 2100 mm, unless raising the head for deeper daylight.
• Use a 900 mm sill as the default in living rooms and bedrooms; choose 1050–1200 mm above kitchen counters.
• Place bathroom ventilators high, at about 1800 mm or more, with the head below the false ceiling.
• Never let a sill fall at counter, desk or headboard height; decide the furniture layout before fixing sills.
• Give every sill below about 900 mm on an upper floor a guard at 1000–1100 mm, fixed safety glass or a restrictor.
• Shade south faces with a 600–750 mm chhajja and east and west faces with fins, reveals or screens.
• Plan two openings on different walls wherever possible for cross-ventilation.

Frequently asked questions

What is the standard window sill height in India?

The standard sill height in Indian homes is 900 mm (about 3 ft) above the finished floor for living rooms and bedrooms. Kitchens use 1050–1200 mm above the counter, bathroom ventilators sit at about 1800 mm or more, and low sills of 450–600 mm are used for window seats or views, with a guard on upper floors.

What is the standard window size for a bedroom?

A 1200 × 1200 mm (4 × 4 ft) or 1500 × 1200 mm (5 × 4 ft) window on a 900 mm sill is standard for a bedroom of about 3000 × 3600 mm. It comfortably exceeds the commonly cited NBC guidance of one-tenth of the floor area, which for that room is about 1.08 m².

How is window area calculated as per NBC?

The commonly cited NBC 2016 guidance is that the aggregate area of openings in a habitable room or kitchen, excluding doors, should be at least one-tenth of the floor area. Multiply the room's length by its width, divide by ten, and compare the result with the total area of the windows. Local bye-laws may modify the figure, so check the applicable regulations.

What should be the height of a kitchen window?

The kitchen window sill should be at least 1050 mm above the floor over a standard 850–900 mm counter, and 1200 mm is more comfortable where a sink tap or hob sits below. A 1200 × 900 mm window at that sill keeps its head on the usual 2100 mm line.

Is a low window sill safe in a high-rise flat?

Only with protection. Any sill below about 900 mm on an upper floor should have a fixed guard at 1000–1100 mm, a fixed lower pane of toughened or laminated glass, or restrictors that limit the opening to about 100 mm. Children's rooms should have restrictors whatever the sill height.

What is the standard size of a bathroom ventilator?

Bathroom ventilators are commonly 600 × 450 mm or 600 × 600 mm, set high with the sill at about 1800 mm or more. Where a false ceiling sits at 2200–2400 mm, a shorter ventilator of 300–450 mm height keeps its head below the ceiling; where a window is not possible, an exhaust fan is used instead.