How to Measure Your Garage Door Opening

How to Measure a Garage Door

Accurate measurements are essential when replacing or installing a new garage door. A small mistake can lead to ordering the wrong size, installation delays, or clearance issues with tracks and openers. This step‑by‑step guide shows you exactly how to measure your garage door opening so you can choose the correct door, track type, and hardware.

What You’ll Need

  • Measuring tape (at least 25 ft)
  • Step ladder
  • Notepad or phone for recording measurements
  • Good lighting

Step 1: Measure the Width

Measure the width of the garage door opening from the inside, left jamb to right jamb.

  • Measure at the widest point
  • Record the measurement in feet and inches
  • Check for uneven framing or bowing

Label this as Measurement A.

Step 2: Measure the Height

Measure the height of the opening from the floor to the bottom of the header.

  • Measure in multiple spots to check for floor unevenness
  • Record the smallest measurement

Label this as Measurement B.

Step 3: Measure the Headroom

Headroom is the space between the top of the opening and the ceiling. This determines what track system and opener you can use.

  • Standard doors need 12–18 inches
  • Low‑headroom kits available for tight spaces
  • Openers may require additional clearance

Label this as Measurement C.

See detailed headroom requirements

Step 4: Measure the Backroom

Backroom is the depth of your garage from the opening to the back wall. This determines whether the door can fully open.

  • Door height + 18 inches is typical
  • Wall‑mount openers reduce backroom needs

Label this as Measurement D.

Learn about backroom & sideroom

Step 5: Measure the Sideroom

Sideroom is the space on each side of the opening for tracks, springs, and hardware.

  • 3–5 inches per side for standard tracks
  • More space needed for torsion springs
  • Check for obstructions like pipes or electrical panels

Label these as Measurements E (left) and F (right).

Step 6: Check for Obstructions

Before ordering a door, inspect the garage for anything that could interfere with installation.

  • Low beams or ductwork
  • Lighting fixtures
  • Storage shelves
  • Garage door opener placement
  • Uneven or sloped floors

Step 7: Inspect the Framing

Make sure the jambs and header are structurally sound.

  • Look for rot, cracks, or water damage
  • Ensure the opening is square
  • Measure diagonally corner‑to‑corner to check for racking

Standard Garage Door Sizes

Most residential garage doors fall into standard size ranges.

Single Doors

  • 8′ x 7′
  • 9′ x 7′
  • 8′ x 8′

Double Doors

  • 16′ x 7′
  • 16′ x 8′

Custom sizes are available for unique openings.

When to Consider a Professional Measurement

If your garage has unusual framing, limited headroom, or a heavy custom door, a professional measurement is recommended.

  • Ensures correct track type
  • Prevents ordering mistakes
  • Often required for warranty coverage

Next Steps

Once you’ve taken your measurements, explore the guides below to choose the right door and prepare for installation.