Actual Size of a 30 x 80 Door | What That Label Really Means

A door labeled “30 x 80” measures about 29.5 inches wide and exactly 80 inches tall — the nominal size is rounded up for standard classification, not the slab’s physical dimensions.

That 30 x 80 marking is the nominal size, industry shorthand for stock doors. The real width is typically trimmed by half an inch so the slab fits inside the frame with even gaps. Knowing the actual size is the difference between a clean install and a hardware store run.

What Does “30 x 80” Actually Measure?

The “30” is the nominal width; the actual slab width is roughly 29.5 inches — about 0.5 inches less for clearance. The “80” is the nominal height; actual height is usually exactly 80 inches, though some manufacturers trim it to 79.75 inches. Standard interior doors are 1⅜ inches thick; exterior doors use 1¾ inches for better insulation and security. This 30 x 80 size, often called a “2/6” door because 30 inches equals 2 feet 6 inches, is the most common standard for interior passage doors in US homes, following the International Residential Code (IRC R311.2).

Measuring for a Replacement: The Right Steps

Never trust the label on the old door alone. Every manufacturer’s tolerance can vary by fractions of an inch. Measure the width across the slab at top, middle, and bottom, using the widest reading. A typical “30” slab comes in around 29.5 inches. Measure the height on both edges, taking the tallest — most are exactly 80 inches. Check the thickness on the edge to see if it’s the interior 1⅜-inch standard or exterior 1¾-inch standard. For a prehung unit, remove the door casing to expose studs, measure the rough opening width at top, middle, and bottom, using the largest number. Do the same for height, from the header to the floor. A 30-inch prehung unit needs roughly a 32-inch rough opening width and 82 to 82.5 inches height.

The Rough Opening: Getting the Numbers Right

A 30 x 80 door needs a rough opening significantly larger to accommodate the frame, hinges, shims, and threshold. For an interior prehung door, the framing must be 32 inches wide and about 82 inches tall. For an exterior 30 x 80 door, it’s typically 32 inches wide by 82.5 inches tall. If your rough opening is exactly 31 inches wide, a standard 30-inch prehung door will not fit — you need a 28-inch or custom door, or reframing. Always confirm the rough opening width at the narrowest point before buying. If you’re ready to shop, our tested roundup of best 80×30 interior doors covers top choices by material and budget.

Compatibility Traps to Avoid

Wrong rough opening for a prehung unit. A 30 x 80 prehung door, including its frame, measures roughly 31.5 to 32 inches wide. If your rough opening is narrower, the frame won’t drop in — a 31-inch opening needs a 28-inch door or stud cutting.

Accessibility minimums. Go wider on main hallways for accessibility.

Older homes and non-standard sizing. Homes built before the early 1990s often used narrower doors (18 to 28 inches) and shorter heights (78 inches). A standard 30 x 80 slab won’t fit a 78-inch rough opening without structural changes — measure before ordering.

Thickness mismatch. An interior slab (1⅜ inches) uses different hinges than an exterior slab (1¾ inches). Mounting an interior door on an exterior frame leaves hinges loose. Stick to the same thickness as the door you’re replacing, or plan to swap the hinges.