At a Glance
A 3×4 window is a rectangular window with a nominal width of 3 feet and height of 4 feet. The actual frame dimensions are slightly smaller, typically around 35.5 inches by 47.5 inches, with the rough opening measuring about 36.5 inches by 48.5 inches. These windows are a common choice for residential bathrooms, hallways, and smaller bedrooms where a standard 3×5 or larger window would be excessive.
For most buyers, the key decision points come down to material (vinyl, aluminum, wood, or fiberglass), operating style (single hung, casement, or sliding), and whether you need a stock size or a custom fabrication. If your opening is non-standard or you are supplying windows for a multi-unit project, factory-direct customization often makes more sense than forcing a stock unit to fit.
Types & Categories
3×4 windows are available in every major operating style, and the style you choose affects both the rough opening requirements and the installed cost.
Single Hung and Double Hung are the most traditional options. A single hung window has a fixed upper sash and a movable lower sash; a double hung allows both sashes to slide. Both are easy to clean from inside and provide good ventilation when opened. For a 3×4 opening, double hung units are common in residential replacements because they match the look of older homes.
Casement Windows are hinged on one side and crank outward. They offer better air sealing than hung windows because the sash presses against the frame when closed. A 3×4 casement is a good choice for hard-to-reach areas like above a kitchen counter or in a stairwell, where cranking is easier than lifting a sash.
Sliding Windows (also called gliders) move horizontally on tracks. They are the most economical option for a 3×4 opening and are frequently used in ranch-style homes or commercial buildings. The trade-off is that only half the window can be opened at any time, and the track system can be less airtight than a casement.
Fixed Windows are non-operating and serve purely as glazing. A 3×4 fixed window is the least expensive option and provides the best energy performance because there are no moving parts to leak air. These are often used in stairwells, bathrooms, or as accent lighting in a wall.
Awning Windows hinge at the top and open outward from the bottom. They are excellent for ventilation during light rain, but they are less common in a 3×4 size than in smaller formats.
Comparison Table
The table below compares the common operating styles for a nominal 3×4 window. Note that actual dimensions and rough openings vary by manufacturer and material, so always confirm with the specific product data sheet before framing.
| Window Type | Typical Actual Size (W x H) | Typical Rough Opening (W x H) | Ventilation | Relative Cost |
|---|---|---|---|---|
| Single Hung | 35.5″ x 47.5″ | 36.5″ x 48.5″ | Lower sash only | Low |
| Double Hung | 35.5″ x 47.5″ | 36.5″ x 48.5″ | Both sashes | Low-Medium |
| Casement | 35.5″ x 47.5″ | 36.5″ x 48.5″ | Full sash opens | Medium |
| Sliding | 35.5″ x 47.5″ | 36.5″ x 48.5″ | Half opens | Low |
| Fixed | 35.5″ x 47.5″ | 36.5″ x 48.5″ | None | Low |
The rough opening dimensions above are industry-typical for a nominal 3×4 window, but they are not universal. Vinyl frames tend to be thicker than aluminum, and wood frames can vary based on the jamb width. Always order the window first, then frame the rough opening to the manufacturer’s specified dimensions.
Buying Factors
Actual vs. Nominal Dimensions
The most common mistake buyers make is assuming a 3×4 window is exactly 36 inches by 48 inches. It is not. The “3×4” designation is nominal, meaning the window is described by its approximate size in feet. The actual frame is typically 1/2 to 1 inch smaller in each dimension to allow for shimming and leveling during installation. The rough opening must be slightly larger than the actual frame — usually 1/2 to 3/4 inch on each side — to accommodate shims and flashing.
For a 3×4 window, expect the actual frame to be about 35.5 inches wide by 47.5 inches high, with a rough opening around 36.5 by 48.5 inches. If you are replacing an existing window, measure the rough opening, not the old window frame, and order accordingly.
Egress and Building Code Compliance
A 3×4 window is often used in bedrooms, which raises the question of egress compliance. Building codes (IRC and IBC) require bedroom windows to meet minimum opening dimensions for emergency escape and rescue. The typical requirement is a net clear opening of at least 5.7 square feet (for ground-floor windows; 5.0 square feet for above-ground with a sill height no more than 44 inches). The clear opening must be at least 24 inches high and 20 inches wide.
A 3×4 window with a double hung or casement operation can meet egress requirements if the sash opens to the full 24-inch height and 20-inch width. However, a sliding window in a 3×4 size often fails egress because only half the width opens, yielding a clear opening of roughly 18 inches — below the 20-inch minimum. Before specifying 3×4 windows for bedrooms, check the local code and the net clear opening of the specific unit. For basement bedrooms, the requirements can be even stricter.
Material Selection
The material you choose affects durability, maintenance, thermal performance, and cost.
Vinyl (uPVC) is the most common residential choice. It is inexpensive, does not require painting, and provides good thermal performance with multi-chambered frames. The downside is limited color options and a tendency to expand and contract with temperature swings, which can affect sealing over time.
Aluminum is the standard for commercial and industrial applications. It is strong, lightweight, and can be extruded into slim profiles that maximize glass area. The major drawback is thermal conductivity — bare aluminum conducts heat readily. For energy-efficient projects, look for thermal-break aluminum, where a polyamide strip separates the interior and exterior frames. This is a standard feature in modern system windows and is essential for projects in colder climates.
Wood offers the best aesthetics and natural insulation, but it requires regular maintenance and is the most expensive option. Wood windows are typically chosen for historic renovations or high-end residential projects where appearance matters more than lifecycle cost.
Fiberglass is a newer option that combines the strength of aluminum with the thermal performance of vinyl. It is dimensionally stable, resists warping, and can be painted. The cost is higher than vinyl but competitive with wood.
Glass Packages
The glass specification often matters more than the frame material for energy performance. A basic 3×4 window with single glazing is rarely acceptable in modern construction. Double glazing with a low-E coating is the minimum standard in most regions. For colder climates, consider triple glazing or argon gas fills. For noise reduction, laminated glass or different glass thicknesses can help.
The U-factor and Solar Heat Gain Coefficient (SHGC) are the key metrics. Lower U-factor means better insulation; SHGC indicates how much solar heat passes through. The right combination depends on your climate zone, and local code will often dictate minimum performance levels.
Price & Cost
The cost of a 3×4 window varies significantly based on material, glass package, and whether you are buying a stock unit or a custom fabrication. As a general range for a mid-grade double-glazed unit:
- Vinyl: $150–$400 per unit
- Aluminum (thermal break): $250–$600 per unit
- Wood: $400–$900 per unit
- Fiberglass: $300–$700 per unit
These are unit prices for the window itself. Installation adds roughly $150–$400 per window depending on whether it is a new construction installation or a replacement (retrofit) into an existing frame. Full-frame replacements cost more than insert replacements because they require removing the old frame and flashing the opening.
For commercial projects or large residential developments, pricing changes significantly. Factory-direct purchasing, where you buy in bulk directly from a manufacturer rather than through a distributor or retailer, can reduce unit costs by 20–40%. This is particularly relevant for aluminum and system windows, where the markup from manufacturer to end-user can be substantial.
Custom sizes cost more than stock sizes because they require a separate production run. The premium is typically 10–25% over a comparable stock window, depending on the complexity of the customization.
Pros & Cons
3×4 Windows
Pros:
- Fits standard residential openings without major framing changes
- Suitable for bathrooms, hallways, and smaller rooms
- Available in all operating styles
- Lower cost than larger sizes like 3×5 or 3×6
Cons:
- May not meet egress requirements for bedrooms, depending on style
- Less natural light than larger windows
- Can look undersized in rooms with high ceilings or large wall areas
Comparing to Other Sizes
A 3×6 window (3 feet wide, 6 feet tall) provides 50% more glass area than a 3×4 and is a better choice for living rooms or primary bedrooms where natural light is a priority. The cost is proportionally higher, and the rough opening is significantly taller.
A 4×3 window (4 feet wide, 3 feet tall) is a horizontal orientation — common in modern architecture for clerestory or transom applications. It offers the same glass area as a 3×4 but distributes it differently. The 4×3 is a good choice for wide walls or above doors.
6×3 windows (6 feet wide, 3 feet tall) are used for picture windows in living rooms or as large fixed panes. They provide a wide view but require a substantial lintel or header to support the weight above the opening.
5×5 windows (5 feet square) are a common choice for stairwells and large bathrooms. They offer a balanced appearance and are available in both fixed and operating configurations.
12×12 windows are oversized units used in commercial applications, sunrooms, or walls of glass in modern homes. These require structural engineering and are typically custom-fabricated.
2×5 windows (2 feet wide, 5 feet tall) are narrow vertical units often used in pairs or triples to create a tall, elegant appearance. They are common in bathrooms and entryways.
40×40 and 40×60 windows are metric equivalents (40 cm x 40 cm and 40 cm x 60 cm) commonly used in international projects, particularly in Asia and Europe. These are roughly 15.7 inches by 15.7 inches and 15.7 inches by 23.6 inches, respectively. If you are working on a project outside the US, confirm whether dimensions are specified in feet/inches or centimeters to avoid ordering errors.
Additional Considerations
Ordering Custom-Sized Windows
If your opening does not match a standard size, you have two options: adjust the framing to fit a stock window, or order a custom window to match the opening. For new construction, adjusting the framing is usually cheaper. For renovations, custom windows avoid the cost and complexity of reframing.
When ordering custom windows, provide the exact rough opening dimensions — not the desired glass size. The manufacturer will subtract the appropriate allowances for frame thickness and installation clearances. Specify the operating style, material, color, glass package, and any hardware requirements. For commercial projects, also specify whether the windows need to meet specific wind load or air infiltration ratings, which may be dictated by local building codes.
Retrofit vs. New Construction
A retrofit (insert) window slides into an existing frame and is secured with screws and expanding shims. This is the less expensive option for replacements because it does not require removing the old frame or disturbing the exterior siding. However, a retrofit window is slightly smaller than the original because it fits inside the old frame, reducing the glass area.
A new construction window has a nailing fin (flange) that attaches to the framing and is flashed to prevent water intrusion. This is required for new buildings and recommended for full-frame replacements where the old frame is removed. The rough opening must be properly sized and flashed before installation.
Measuring Like a Pro
When measuring for a 3×4 window replacement, measure the rough opening at three points: top, middle, and bottom for the width; and left, center, and right for the height. Use the smallest measurement for ordering. Check that the opening is square by measuring diagonals — they should be within 1/4 inch of each other. If the opening is out of square, a custom window can be made to fit, or the framing can be adjusted.
How We Meet These Standards
As a manufacturer, our approach to the 3×4 window segment is straightforward: we build to the opening, not the other way around. Our factory in China produces thermal-break aluminum windows, system windows, and custom villa windows in any size, including 3×4 and metric equivalents like 40×40 and 40×60. Because we sell factory-direct, the pricing reflects the manufacturing cost, not a distributor’s markup.
For buyers managing multi-unit projects, we offer full customization on size, color, glass, and hardware. We also adjust profile structures and fittings to match the building codes of your target market — a critical step when importing windows for a project in a different country. Every unit undergoes pre-shipment testing for air-tightness, water-tightness, and wind resistance, and we provide the full documentation package needed for customs clearance.
If you are comparing suppliers for a project that requires 3×4 windows or custom sizes, the questions worth asking are: Can you match the local code requirements? Can you produce non-standard sizes without a large premium? And what is the lead time for a production run? If the answer to those questions matters for your project, it is worth getting a quote from us.
