How Big Is 300 Square Feet? Real Dimensions and Uses

300 square feet is a room about 15 by 20 feet, or 17 feet 4 inches on a side, roughly 27.9 square meters. That is a quarter larger than a standard one-car garage, and about one-seventh of the 2,142-square-foot median new American single-family home. Small, but a legal dwelling in California.

Sizing up: how big 400 square feet is and how big 1,000 square feet is.

What are the dimensions of 300 square feet?

Most often 15 by 20 feet. Any length times width that comes to 300 works, so the shape is yours:

• 15 × 20 ft: common
• 12 × 25 ft: narrow
• 10 × 30 ft: long and narrow
• 16 × 18 ft 9 in: nearly square
• 17 ft 4 in square: square

In other units: 27.87 square meters, 33.33 square yards, or 43,200 square inches.

Is 300 square feet bigger than a one-car garage?

Yes, by 25 percent. The claim you see everywhere, that a one-car garage is about 300 square feet at 12 by 20, does not survive multiplication: 12 × 20 is 240, the standard one-car garage. A better anchor: the interior floor of a 40-foot shipping container, about 304.7 square feet, within 2 percent.

What fits in 300 square feet?

A studio apartment's floor plan: one habitable room, a compact kitchen run, and a walled bathroom. Code sets the floor: a habitable room needs 70 square feet and 7 feet in every horizontal dimension. That leaves one room plus a bath, not two bedrooms, which is why the studio ADU works here. Separate the areas with rugs and a bed that stores underneath instead of walls, run storage up the walls, and put windows on two sides so natural light makes one room read as two.

Can you build a 300-square-foot ADU in California?

Yes. The state's floor for an efficiency dwelling unit is 150 square feet of living space with a separate closet, small kitchen and separate bathroom. No California city can refuse a 300-square-foot unit for being too small. Size is not the constraint here; setbacks, height, lot coverage and the 7-foot ceiling minimum still are. Two thresholds sit above this size: ADUs under 750 square feet are exempt from local impact fees, and school impact fees apply only above 500. This size clears both. A JADU inside the main house is capped at 500 square feet; converting an existing accessory structure has no size limit. The rules now sit in Government Code §§ 66310–66342, not the repealed § 65852.2, collected in the HCD ADU Handbook. More on backyard tiny house sizes and permits and ADU building permit costs.

How to measure 300 square feet yourself

Length times width, in feet. Break an L-shaped room into rectangles, measure each with a tape, add them. Inches divide by 12; square inches divide by 144. Only floor area under a 7-foot (and above) ceiling counts as finished square footage, and a garage never counts. Ordering flooring? Add 5 percent for vinyl, 10 percent for hardwood. Use our ADU Viewer app for iPhones and iPads to view in your backyard.