Construction glossary · Units of measure

What is gaugein construction?

In construction, gauge is a number that indicates the thickness of sheet metal, including metal studs, roof deck, and flashing, and the scale runs backward: the higher the gauge number, the thinner the metal. A 25 gauge stud has a minimum base metal thickness of about 0.0179 in, while a 20 gauge structural stud is about 0.0329 in, nearly twice as thick. Estimators read gauge callouts on wall types, framing schedules, and specs because lower gauge (thicker) material costs more and is required where walls carry load or exceed limiting heights.

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Updated June 2026 · Reviewed by the Ruh construction team

Lower number = thicker steel18 ga = ~0.048 inUsed for studs, duct, decking

Sheet-metal gauge scale (lower = thicker)

The definition

Gauge, explained.

Gauge is the traditional US system for calling out sheet metal thickness, and it shows up all over a commercial bid set: partition schedules (25 ga interior studs), cold-formed framing schedules on the structural sheets (20 ga, 18 ga, 16 ga), roof deck notes (22 ga or 20 ga), hollow metal frame specs (16 ga), and flashing details (24 ga). The number maps to a decimal thickness through published tables, and the scale runs opposite to instinct: 25 ga is thinner than 20 ga, and 16 ga is thicker than both. The stud industry has largely moved to mil designations (1 mil = 0.001 in), so specs often pair the two: 25 ga is 18 mil, 20 ga drywall is 30 mil, 20 ga structural is 33 mil, 18 ga is 43 mil, and 16 ga is 54 mil. New estimators get burned three ways: assuming a higher gauge number means heavier material, treating the two different 20 gauge studs as the same product, and pricing a whole job at 25 ga when the drawings call for heavier gauge at tall partitions, jamb studs, ceilings, and backing.

How it is measured

Gauge itself is unitless; each number corresponds to a decimal inch thickness in a published table, and the tables differ slightly by material (standard steel, galvanized, stainless, aluminum). For cold-formed studs the controlling value is minimum base metal thickness in mils: 18 mil (25 ga) is 0.0179 in, 33 mil (20 ga structural) is 0.0329 in, and 43 mil (18 ga) is 0.0428 in. Look for gauge on wall type tags, the cold-formed framing schedule, deck notes, and in spec sections 05 40 00 and 09 22 16. Estimators do not measure gauge at bid time; they read it off the documents, then carry each thickness as its own takeoff line item, because every gauge is a different SKU with its own unit cost and labor production rate.

Worked example

A worked gauge example.

Worked example

Say a tenant build-out has 200 lf of corridor partition framed to a 14 ft deck with 3 5/8 in studs at 16 in on center. Stud count: 200 lf x 12 / 16 in = 150 studs, plus one to close the run; call it 155 after corners and door jambs. The wall type calls 25 ga (18 mil, 0.0179 in minimum thickness), but the manufacturer's limiting height table for that stud at 16 in spacing tops out around 13 ft, so a 14 ft wall needs 20 ga structural (33 mil, 0.0329 in). That is 0.0329 / 0.0179 = about 1.8 times the steel. Material check, illustrative US pricing: 155 studs x 14 ft = 2,170 lf. At $0.85 per lf for 25 ga, material runs $1,845; at $1.55 per lf for 20 ga, it runs $3,364. Missing the gauge bump costs about $1,519 on one corridor, before the heavier-gauge labor premium.

How Ruh handles it

How Ruh handles gauge.

Ruh reads the wall types and framing schedules on the contractor's drawings, so a partition tagged 20 ga structural and one tagged 25 ga land in the takeoff as separate line items instead of one blended stud quantity. It then prices each gauge against the contractor's own price book, using their real unit costs for 18 mil versus 33 mil material. The estimator still makes the judgment calls, like flagging a 14 ft wall that exceeds a 25 ga limiting height, then reviews, adjusts, and signs off on the draft.

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Gauge: frequently asked questions

Why does a higher gauge number mean thinner metal?+

The system traces back to early wire and sheet production, where the number roughly tracked how many drawing passes it took to reach a size, and more passes meant thinner stock. The numbers stuck even after manufacturing methods changed. Modern framing specs increasingly use mil thickness (1 mil = 0.001 in) instead, which reads in the intuitive direction: bigger number, thicker steel.

What is the difference between 20 gauge drywall studs and 20 gauge structural studs?+

They are different products that share a name. A 20 ga drywall stud is 30 mil (0.0296 in minimum) and is limited to non-structural interior work, while a 20 ga structural stud is 33 mil (0.0329 in minimum) and is rated for load-bearing conditions, exterior walls, and jamb framing. If a spec says 20 ga, check whether it references 30 mil or 33 mil before pricing, because the structural version costs more and is not always substitutable.

Does gauge mean the same thickness for every metal?+

No. Standard steel, galvanized steel, stainless steel, and aluminum each use different gauge tables, so 20 ga galvanized sheet (about 0.0396 in) is not the same thickness as 20 ga standard steel sheet (about 0.0359 in). That is one reason deck, flashing, and stud submittals list decimal or mil thickness. When reviewing a substitution, compare decimal thicknesses, not gauge numbers.

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What is gaugein construction?

Gauge, explained.

A worked gauge example.

Worked example

How Ruh handles gauge.

Gauge: frequently asked questions

Related terms

Knowing what gauge means is the easy half.

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Put your next takeoff on Ruh.