Start by drawing a simple floor plan of your balcony, patio, or rooftop. Measure the longest length and widest width at floor level, then note any awkward corners, pillars, railings, drains, or built-in planters. Don't rely on memory or old listings—use a tape measure and write everything down in the same unit, ideally centimeters or inches. If you live in an apartment, also measure the path the furniture has to travel: door width, hallway turns, elevator depth, and stair clearance. A sofa that fits on the balcony is no good if it can't get through the front door.
Then measure vertical space. Check railing height, overhead structures, and any restrictions if you want an umbrella or tall shelving. For urban outdoor furniture, depth matters as much as width: a compact chair may still feel cramped if it leaves no room to walk. As a rule, leave at least 18–24 inches (45–60 cm) of walking space around main seating, and more if people will pass through regularly. Use painter's tape on the floor to mark the furniture footprint and the clearance zone. Sit in the taped area, imagine moving around it, and test whether doors or windows can still open.
Next, account for how you'll use the space. If you want a small dining set, measure the table plus pulled-out chairs. For loungers, include the space to recline. Think about sun, wind, rain, and privacy, especially on high-rise balconies, and leave room for plants or storage if needed. Take photos with the tape measure visible, and keep a simple list of maximum length, width, and height for each piece. Check building rules for weight limits, fire exits, and furniture materials too. Buying urban outdoor furniture is much easier when you shop with exact numbers and a realistic layout—not just a style photo.