Hollow Metal Door Gauges: 20, 18, 16 and 14 Explained
Hollow metal door gauge is the thickness of the steel face. A lower number means thicker steel. Under ANSI/SDI A250.8, the standard door faces are 20 gauge (Level 1), 18 gauge (Level 2), 16 gauge (Level 3) and 14 gauge (Level 4). Frames follow a different table. Gauge also says nothing on its own about fire rating.
This guide shows what each gauge measures, which one fits which opening, and what to check before you order a replacement.
TL;DR
- Door faces: 20 gauge is 0.032 in minimum, 18 is 0.042 in, 16 is 0.053 in, 14 is 0.067 in, per ANSI/SDI A250.8.
- Gauge is tied to a duty level. Specify the level and model, not just a gauge number.
- Frame gauges differ from door gauges. Level 1 frames are 18 gauge, Levels 2 and 3 are 16 gauge, Level 4 is 14 gauge.
- A thicker face does not make a door fire rated. Only a labeled, listed assembly does.
- Gauge is the face thickness, not the overall thickness of the door leaf.
Table of Contents
- What gauge actually measures
- Door gauge by SDI level
- Frame gauges are a different table
- Choosing a gauge for the opening
- Gauge does not make a door fire rated
- Gauge is not the only number to check on a replacement
- Perspective: how we choose a gauge
- Order doors, frames and hardware from us
- Spec checklist before you buy
- FAQ
- Sources
What gauge actually measures
Gauge is a legacy way to describe sheet steel thickness. The Steel Door Institute notes that the term is no longer common for defining material thickness, yet it is still used when specifying doors and frames. So you will see both gauge and decimal inches on submittals.
Two points cause most confusion:
- Gauge is the face, not the door. A 16-gauge door has a steel face of 0.053 in minimum. The finished leaf is much thicker, and its thickness depends on construction, core, edge design and hardware preparation. Do not infer one from the other. See the SDI selection guide.
- Lower number, thicker steel. 14 gauge is heavier than 18 gauge. The difference in minimum thickness between 20 and 14 gauge is more than double.
Door gauge by SDI level
The standard groups doors into four levels. The ANSI/SDI A250.8 standard names them standard, heavy, extra heavy and maximum duty.
| Level | Duty | Door face gauge | Minimum thickness |
|---|---|---|---|
| 1 | Standard | 20 | 0.032 in (0.8 mm) |
| 2 | Heavy | 18 | 0.042 in (1.0 mm) |
| 3 | Extra heavy | 16 | 0.053 in (1.3 mm) |
| 4 | Maximum | 14 | 0.067 in (1.7 mm) |
You may see slightly different decimals on manufacturer charts, such as 0.035 in for 20 gauge. Those are nominal manufacturer’s standard gauge values. The table above uses the minimum steel thickness the standard lists. Check which one your specification calls for.
The levels trade thickness, weight, durability and cost against expected use. That is why “best gauge” has no single answer.
Frame gauges are a different table
A common mistake is assuming the frame matches the door. It does not. The same standard lists minimum frame thickness separately:
| Level | Frame gauge | Minimum thickness |
|---|---|---|
| 1 | 18 | 0.042 in (1.0 mm) |
| 2 | 16 | 0.053 in (1.3 mm) |
| 3 | 16 | 0.053 in (1.3 mm) |
| 4 | 14 | 0.067 in (1.7 mm) |
Frame requirements can also vary with interior or exterior conditions and frame type, so the project specification and approved product listing control. Source: ANSI/SDI A250.8.
In practice, 16 gauge is the common commercial frame. Our welded steel door frames and knock-down steel door frames are both 16 gauge hollow metal. If you are unsure which frame type suits the wall, our guide to hollow metal door frame types and profiles covers it.
Choosing a gauge for the opening
Start with how the door will be used, then confirm the specified level. These are practical starting points, not code requirements.
20 gauge (Level 1)
A recognized standard-duty option. It can suit low-wear openings when the project specification permits it. It is not automatically right for high traffic, abuse, security or every fire-rated opening. Source: SDI selection guide.
18 gauge (Level 2)
A step up for interior doors with regular use. Think offices, storage rooms and light-traffic corridors.
16 gauge (Level 3)
The usual choice for heavy traffic and exterior openings: stairwells, mechanical rooms, back-of-house doors, and common areas in multifamily buildings.
14 gauge (Level 4)
For high-abuse or high-security conditions: loading areas, institutional settings, and similar openings. It is also the heaviest door to hang, so confirm hinges and frame can carry it. Sizing hardware to the weight it carries is a general principle, as this hardware selection guide explains for gates.
Weigh these factors together:
- Traffic volume and likelihood of impact from carts, equipment or vandalism.
- Interior or exterior exposure.
- Security needs.
- Hardware weight and reinforcement.
- Fire rating requirement for the opening.
- Budget. Thicker steel costs more and weighs more.
Gauge does not make a door fire rated
This matters most to our readers. A 14-gauge face is not a substitute for a listed fire door assembly.
Fire-rated doors and frames should be selected as labeled assemblies tested under applicable standards such as NFPA 252, UL 10B or UL 10C, according to NAAMM’s fire-rated hollow metal guidance. The required rating, temperature-rise or smoke-control feature, and listing depend on the opening and the governing jurisdiction.
The door, frame, hardware, glazing where present, and installation must all match the listed assembly and its label. Swapping a part means verifying it against the listing and local requirements. In New York City, ask your architect, expediter or the building’s fire safety professional what rating each opening needs before you order.
Gauge is not the only number to check on a replacement
A door with the right gauge can still fail to latch or swing if the opening is wrong. The standard treats clearances separately from gauge tables.
- Door-to-frame clearance: generally limited to 1/8 in (3.2 mm) at the listed locations for single-swing doors and pairs, per the A250.8 PDF. Bottom clearance is addressed separately.
- Undercut: the standard maximum from the bottom of the door to the bottom of the frame is 3/4 in (19.1 mm) unless otherwise specified, per ANSI/SDI A250.8. That is a general figure. Fire door undercuts must comply with NFPA 80 and the listed assembly. Never trim a rated door in the field based only on the general maximum.
- Hinges and alignment: check hinge locations, reinforcement and frame plumb before ordering. Precision in hole and edge placement matters on any sheet metal part, as this note on hole-to-edge distance shows.
Measure the existing opening in the field. Do not rely on drawings alone.
Perspective: how we choose a gauge
We see the same mistake on rush orders: someone asks for “a 16-gauge door” and nothing else. Gauge is one line in a spec. We ask what the opening needs to do. What rating does it carry? How heavy is the traffic? What hardware goes on it? Is the frame already in place?
For fire-rated work, we start from the label and the listed assembly, then confirm gauge. A thicker sheet is not a shortcut to compliance, and it can make a hang harder if the hinges and frame were not built for it. For frames, we stock 16 gauge in welded and knock-down types, since that is what most commercial openings call for.
When the schedule is tight, getting the details right the first time saves more time than any fast truck. That is why we pair supply with installation and service.
— Esteban
Order doors, frames and hardware from us
Universal Fireproof Doors manufactures and supplies fire-rated steel doors, hollow metal doors, hollow metal frames and commercial door hardware, with installation and emergency replacement and repair service. We offer same-day or next-day delivery, custom sizing and bulk order discounts for contractors and property managers. Our products are made with NYC fire and safety standards in mind.
If you need a complete opening, see our steel door units with frame, self-closing hinges and cylindrical lockset, or browse everything at ufdoors.com. Send us your opening sizes, rating and duty level and we will help match the right products.
Spec checklist before you buy
- Required fire rating for each opening, from the drawings or the authority having jurisdiction.
- SDI level and model, not only gauge.
- Door face gauge and frame gauge, listed separately.
- Frame type: welded or knock-down, and the wall condition.
- Hardware preparation, hinge reinforcement and any closers.
- Field-measured opening size and swing.
- Current edition of the governing standard and project specification. NAAMM’s HMMA division publishes guide specifications for hollow metal doors and frames and for their receipt, storage and installation, so rely on those and the project spec rather than a generic gauge chart.
FAQ
What gauge are hollow metal door frames?
It depends on the level. Under ANSI/SDI A250.8, Level 1 frames are 18 gauge, Levels 2 and 3 are 16 gauge, and Level 4 is 14 gauge. Sixteen gauge is the most common for commercial work. The project specification and listing control.
How thick is a 16-gauge hollow metal door?
The steel face is 0.053 in (1.3 mm) minimum, per the SDI selection guide. That is the face only. The overall leaf is thicker and depends on construction, core and edge design.
Is a 20-gauge steel door good?
It is a recognized Level 1 standard-duty option with a 0.032 in minimum face. It can work for low-wear openings when the specification allows it. It is not automatically suited to heavy traffic, abuse, security or every fire-rated opening.
What is the standard undercut for a hollow metal door?
The general maximum is 3/4 in (19.1 mm) from the door bottom to the frame bottom unless otherwise specified. Fire doors are different. Their undercut must meet NFPA 80 and the listed assembly, so do not trim a rated door on the general figure alone.
Sources
- ANSI/SDI A250.8 Steel Door Standard
- ANSI/SDI A250.8 full specification (PDF)
- SDI-108 Selection & Usage Guide for Standard Steel Doors
- NAAMM: Fire Rated Hollow Metal Doors & Frames
- NAAMM: HMMA division