January 5, 2026 7 min read Voluntown Garage Doors Team
# Size Measurement Guide: What Every Homeowner Should Know
Whether you're replacing an existing garage door or planning a new installation, accurate measurements are crucial for a successful project. At Voluntown Garage Doors, we provide free in-home consultations where our experts take precise measurements. However, understanding the measurement process helps you prepare for your consultation and ensures you can provide accurate information when requesting a quote.
Garage doors are custom-fitted to your specific opening. Unlike many home improvement products that come in standard sizes, garage doors must precisely match your opening for proper operation, security, and appearance. A door that's too small leaves gaps that compromise insulation and security. A door that's too large simply won't fit.
Standard residential garage doors typically come in widths of 8, 9, 10, 12, 14, 16, and 18 feet, with heights ranging from 7 to 8 feet. However, many homes, especially older ones or custom builds, have non-standard openings that require specially ordered doors.
Start by measuring the width of the opening at its widest point. Measure from inside the left jamb to inside the right jamb at floor level. Take this measurement at least twice to ensure accuracy, and if you get different readings, use the larger measurement.
For the most accurate results, also measure the width at the middle and top of the opening. If there's significant variation (more than an inch), the frame may need adjustment before a new door can be installed.
Measure the height from the garage floor to the bottom of the header (the horizontal framing member above the opening). Like width, take this measurement at both sides and in the middle. Use the largest measurement and note any significant variations.
If you're considering a taller door to accommodate a larger vehicle or equipment, verify that you have adequate headroom above the existing opening to accommodate the new door's tracks and mechanism.
Headroom is the space between the top of the door opening and the ceiling or any obstructions. This measurement determines what type of opener and track system can be used. Most standard torsion spring systems require 12-15 inches of headroom, though low-headroom kits are available for spaces with limited clearance.
Side room is the wall space on either side of the opening. Standard track systems require 3-4 inches of side room, though this can vary based on the door type and opener system. Take accurate measurements to ensure your new door and tracks will fit.
Backroom is the depth of the garage from the door opening to the back wall or any obstruction like a car parked inside. The door needs enough backroom to fully open and stack. A general rule is that you need backroom equal to the door height plus 18 inches, though this varies by door type.
Different garage door styles have different installation requirements. Traditional sectional doors have the most flexible installation options and can work with limited headroom or backroom using special hardware.
Contemporary aluminum doors with full glass panels, a popular choice among our customers, typically require standard headroom but may need additional structural support due to their weight. Our team can assess your garage during a free consultation and recommend any necessary modifications.
If you're upgrading from an older one-piece tilt-up door to a modern sectional door, your opening dimensions might need adjustment. The track system for sectional doors differs significantly from tilt-up mechanisms.
For commercial properties or garages housing RVs, boats, or other large vehicles, measurement becomes even more critical. Commercial doors can exceed 20 feet in width and require heavy-duty hardware and opener systems.
When measuring for oversized openings, pay special attention to structural considerations. Large doors are heavy and place significant stress on the surrounding structure. Our commercial door experts can assess whether your existing framing is adequate or if reinforcement is needed.
Don't measure with the old door still in place unless you're confident it was correctly sized. Previous installers may have made errors or used non-standard sizing.
Don't forget to account for the floor. If you're planning to add a new concrete apron or resurface the garage floor, factor this into your height measurement.
Don't ignore level and square. If your opening isn't level and square, the new door will need adjustment or the opening will need correction. Check with a level and measure diagonals to verify the opening is square.
While this guide provides the basics for measuring your garage door opening, nothing replaces a professional assessment. At Voluntown Garage Doors, we offer free in-home consultations where our experts measure your opening with precision tools, assess structural considerations, and help you select the perfect door for your home.
With 22+ years of experience and over 4,981 satisfied customers, we've seen every possible garage configuration. Let us put that expertise to work for you. Contact us today to schedule your free consultation and take the first step toward your new garage door.