What size screws for internal doors?

When installing or replacing internal doors in your home, using the proper screw size is important for stability and safety. The screw size depends on the type and thickness of the door, the frame material, and whether you need to go into a wall stud. Using screws that are too small can lead to a loose door that sags over time, while screws that are too large can split the door frame. Finding the right balance requires understanding door components, common screw sizes, and best practices.

Common Internal Door Thicknesses

Interior doors typically come in four standard thicknesses:

• 1-3/8 inches – Hollow core interior doors for bedrooms and closets
• 1-3/4 inches – Solid core doors for heavily used rooms like kitchens and bathrooms
• 1-3/8 to 1-1/2 inches – Interior panel and barn doors
• 2-1/4 inches – Heavy duty commercial interior doors

The most common interior door thickness for homes is 1-3/8 inches. Heavy duty solid core doors are 1-3/4 inches thick. When selecting screws, match them as closely as possible to the door thickness without going over.

Interior Door Frame Types

There are two main types of interior door frames to consider when choosing screw size:

• Wood frames – Most interior doors use traditional wood frames. These include various species like pine, poplar, oak, and more. For wood frames, target the screw size to match the door thickness.
• Metal frames – Some interior doors use metal frames for added durability and fire safety. These are common in commercial buildings but also found in some homes. Metal frames require smaller screw sizes to avoid splitting the frame.

You’ll also need to consider whether the frame material is softwood or hardwood. Softer woods like pine allow larger screw sizes while dense hardwoods like oak require smaller screws to avoid cracking.

Standard Interior Door Screw Sizes

Here are the most common screw sizes used for installing interior doors to match various door thicknesses and frame materials:

Screw Size	Best Use
#6 x 1-1/4 in	1-3/8 in hollow core doors into wood frames
#8 x 1-1/2 in	1-3/4 in solid core doors into wood frames
#6 x 1 in	Any interior door into metal frame
#8 x 2-1/2 in	Extra long screws going into wall stud

The most commonly used screw is a #6 x 1-1/4 inch for typical 1-3/8 inch hollow core doors installed into wood frames. Go up one size to #8 x 1-1/2 inches for thicker solid core doors. When installing into metal door frames, use smaller #6 screws around 1 inch to avoid splitting the frame.

If you need extra strength going into a wall stud, use long 2-1/2 inch screws in a larger #8 size. Pre-drilling the holes will prevent splitting.

How to Choose the Right Screw Size

Follow these tips when selecting screws for interior doors:

• Match the screw length to the door thickness. Go slightly under the thickness.
• Use smaller screws with metal frames to prevent cracking.
• Softwoods can handle larger screws than hardwoods.
• Turn screws by hand first to check for binding before power driving.
• Pre-drill holes for dense woods and longer screw lengths.

Having screws that are too long or too large in diameter for the frame material can cause unsightly cracking. Test fit screws and check that they go into the solid portion of the frame or wall stud without fully poking through.

Aim for a screw size that fills at least half of the door’s thickness when driven flush. This gives enough holding power without risk of poking through the other side. Don’t rely solely on drywall for grip. Always try to hit a stud.

How Many Screws Per Hinge?

For each hinge, you should install:

• 2 screws in the door frame side
• 2 screws in the door slab side

This totals 4 screws per hinge. Use the same sized screw for both the frame and door. Having fewer screws can lead to loose hinges over time as the weight of the door pulls down. For heavier solid core doors, some installers use 3 screws per hinge side for added stability.

If possible, position the screws diagonally from each other rather than in a straight vertical line for better grip. Make sure screws are fully tightened but take care not to strip the head. Leave hinges slightly loose until all are in place so you can adjust the door position, then tighten everything down.

Choosing the Right Hinge Size

The size of hinge you choose also impacts door stability:

• Doors under 30 inches wide can use standard 2.5 inch hinges
• Doors 30 to 36 inches wide do better with 3 inch hinges
• Extra wide doors may require special 4 inch hinges

Bigger hinges provide more support under the weight of the door. For hollow core doors under 30 inches wide, standard hinges are usually sufficient with the proper screw size. But heavier solid core and wider doors benefit from larger hinge sizes.

Tips for Proper Screw Placement

Proper screw placement ensures maximum holding strength:

• Drive screws into the solid center of frame and door stiles.
• Aim for untreated wood rather than laminates or door face materials.
• Position screws diagonal from each other, not vertically lined up.
• Maximize grip by driving screws horizontally into the frame rather than angled up/down.
• Pre-drill pilot holes to prevent wood splitting, especially near ends of the frame.

Positioning screws in the right spots gives better traction and reduces the chance of tearing out wood around the screw head. This is especially important in the door frame stile, where almost all the weight load is placed. Properly driving screws prevents loose hinges and a sagging door down the road.

How Deep to Sink Screws

Here are some screw sinking tips:

• Drive screws flush into the surface without counter-sinking.
• Turn screws by hand initially before power driving to check depth.
• Set adjustable clutch on drill to avoid over-sinking screws.
• Consider color matched screw heads to hide screws.

For the cleanest finish, sink screws flush to the surface so heads sit flat against the frame or door. Avoid over-sinking screws too deep below the surface, as this can weaken the grip. Use care when using power drivers, starting screws by hand first and adjusting clutch settings to a proper depth.

How to Replace Loose Door Screws

If an interior door develops loose screws over time, follow these steps:

1. Inspect to determine source of looseness – hinge, strike plate, or just needs tightening.
2. Open door to access hinge screws. Remove any loose screws.
3. Fill old holes with wood filler and let dry completely.
4. Pre-drill new pilot holes for screws slightly offset from original holes.
5. Drive in new screws flush to surface and check door for tightness.
6. Fill old holes and finish surface with wood filler, sand, and paint.

Look for any wood cracks or splits around old holes. If the frame itself is damaged, you may need to patch in a wood repair block before drilling new holes. Change to a longer screw size if originals were too short.

Conclusion

Choosing the proper screw size for interior doors mainly involves matching the length to the door thickness and using thinner screws with metal frames. The most common sizes are #6 for hollow core doors and #8 for solid core. Allowing half the screw length to grip into the frame provides optimal strength. Take care when sinking screws to avoid cracking wood around holes. Proper placement diagonally in the door stile and frame plus using adequate hinges for the door width also prevents sagging. Check that all screws are tight after installing. If screws loosen over time, replace with new offset holes to regain a solid connection. Taking the time to select and install the optimal screw sizes leads to secure interior doors that function smoothly for years.