To measure a gate opening, you need the distance between the two posts (or walls, columns, or pillars) measured at the inside faces. This single measurement, called the “rough opening,” is the starting point for choosing or ordering the right gate. But getting it right means accounting for hardware gaps, ground slope, and the type of gate you’re installing. Here’s how to do it properly.
Measuring the Rough Opening
The rough opening is the clear space between whatever the gate will attach to, whether that’s wooden posts, brick columns, or stone pillars. Measure from the inside face of one post to the inside face of the other. Don’t measure from the centers of the posts or from the outside edges.
Take this measurement at three points: near the top, at the middle, and near the bottom. Posts can lean or shift over time, especially wooden ones, so you may get slightly different numbers. Use the smallest of the three measurements as your working number. This ensures the gate will fit at the tightest point.
Use a steel tape measure rather than a cloth one. For openings wider than about 6 feet, it helps to have a second person hold the other end so the tape stays taut and level. If you’re measuring between masonry columns, hook the tape on the inside edge of one column and pull it straight across to the other.
Accounting for Hinge and Latch Gaps
Your gate will be smaller than the rough opening. Hinges need room to pivot, and the latch side needs a gap so the gate can swing freely without scraping the post. These gaps vary depending on your hardware. A typical latch gap runs about 3 inches, though dual gates with certain latch types may need a combined gap of 3.25 to 4.25 inches between the two gate panels.
The formula works in both directions. If you already have posts in the ground and need to order a gate, subtract the total hinge and latch clearance from your rough opening to get the gate panel size you need. If you’re buying a gate first and then setting posts, add the hinge and latch gaps to the gate width to determine where your posts should go. Most gate manufacturers list the required gaps for their hardware in the product specifications, so check those before you dig any holes.
Measuring Height and Ground Clearance
Height matters as much as width. Measure from the ground to the top of where you want the gate to sit. Most gates need at least 2 to 3 inches of clearance at the bottom so they don’t drag on the ground when opening and closing. If your driveway or path has gravel, leaves, or snow buildup, you may want more.
On flat ground, this is straightforward. On sloped ground, it gets more involved because the gate needs to clear the highest point of the slope as it swings open.
Handling Sloped or Uneven Ground
If the ground slopes from one post to the other (a side-to-side slope), you need to know the height difference. Tie a string to the base of the higher post, stretch it to the lower post, clip on a small line level (available for a few dollars at any hardware store), and raise the string until the bubble reads level. Measure the distance from the string down to the ground at the lower post. That’s your slope drop. If the drop is 5 inches or less, most gate builders can handle it by angling the bottom rail of the gate to follow the slope.
If the ground slopes from front to back (meaning the driveway rises as it goes toward your house), the gate needs to be hung high enough to clear the rising ground when it swings open to 90 degrees. To figure out how much clearance you need, take a straight board that’s the same length as one gate panel. Set one end at the hinge post on the ground and swing the other end in the arc the gate would travel. Use a level on the board, raise the post end until it reads level, and measure from that raised end down to the ground. That distance tells you the minimum height the gate must be hung above grade to swing freely.
Measuring for Double (Dual) Gates
Double gates split the opening into two panels that meet in the middle. Measure the full rough opening the same way as a single gate, post to post. Then divide by two to get the approximate size of each panel, but remember to subtract the gaps: you’ll have a hinge gap on each side plus a meeting gap in the center where the two panels come together.
Standard residential driveway gates typically range from 10 to 12 feet wide for a single gate and 12 to 16 feet for a double gate. If you need two vehicles to pass side by side, plan for 14 to 20 feet of total opening width. These are the sizes most manufacturers stock, so measuring close to one of these standard widths can save you from a custom order.
Measuring for Sliding Gates
Sliding gates don’t swing, so you don’t worry about arc clearance. But they introduce a different requirement: return space. The gate has to slide completely out of the opening, which means you need clear wall or fence line beside the opening for it to retract into.
The gate panel itself is wider than the opening because it needs an “overhang” section that keeps the gate covering the last bit of the opening when closed. A common rule is to add about 800mm (roughly 31 inches) to your opening width to get the total gate panel size. So a 4-meter opening (about 13.5 feet) would need a gate panel around 4.9 meters long.
The total clear space you need along the fence line is the opening width plus the full gate panel length. Using that same example: 4 meters of opening plus a 4.9-meter panel means you need about 9 meters (just under 30 feet) of total linear space. Measure this return area carefully. Look for anything that would block the gate’s path: downspouts, meters, light fixtures, or changes in the fence line.
Pedestrian Gate Sizing
Pedestrian gates for walkways and garden paths are simpler but have one important threshold. If the gate needs to be wheelchair accessible, the minimum clear opening width is 32 inches. That’s the usable space when the gate is open, not the rough opening between posts. After accounting for hinges and hardware, your rough opening will need to be a few inches wider than 32 inches to meet that standard.
For general foot traffic without accessibility requirements, most pedestrian gates run 3 to 4 feet wide. Measure the path or walkway width leading up to the gate so the opening matches. A gate that’s narrower than the path creates a bottleneck; one that’s wider looks out of proportion.
Tools and Tips for Accurate Measurements
- Steel tape measure (25 feet): Long enough for most residential openings and won’t stretch like cloth.
- Line level and string: Essential for sloped ground. A standard carpenter’s level works too if it’s long enough or if you set it on a straight board.
- Notepad or phone: Write down every measurement immediately. Label which number is width, height, slope drop, and ground clearance.
- Second person: For any opening over 6 feet, an extra set of hands keeps the tape straight and makes the job faster.
Measure twice and record both numbers. If they don’t match, measure a third time. Posts that look square and plumb from a distance can be off by an inch or more, and that inch is the difference between a gate that swings smoothly and one that binds against a post every time you close it.