U.S. aluminum ladders carry one of five duty ratings, and the numbers are not suggestions: Type IAA is rated to 375 lb, Type IA to 300 lb, Type I to 250 lb, Type II to 225 lb, and Type III to 200 lb of maximum safe load [S1][S3].
The duty rating is the maximum safe load capacity of the ladder, defined as the sum of the user's body weight, clothing and protective equipment, the tools and supplies being carried, plus any tools and supplies stored on the ladder itself [S1]. For an aluminum ladder, that figure is stamped on the side rail and corresponds to the ANSI/ALI A14 construction class the manufacturer tested to.
The Five Duty Classes, With Their Load Numbers
The American Ladder Institute lists the five categories in this order: Type IAA (Extra Heavy Duty) 375 lb, Type IA (Extra Heavy Duty) 300 lb, Type I (Heavy Duty) 250 lb, Type II (Medium Duty) 225 lb, and Type III (Light Duty) 200 lb [S1]. Independent reference pages align: Home Depot's buying guide shows Type 3 at 200 lb (household) and Type 2 at 225 lb (medium duty) [S2], while ErectaStep's terms page repeats the 375/300/250/225/200 ladder with the matching duty labels Special, Extra Heavy, Heavy, Medium, and Light [S3]. Lowe's buying guide independently confirms Type IAA at 375 lb and Type IA at 300 lb [S7].
Two things to note on nomenclature. First, the "Roman numeral" ladder (I, IA, IAA) is the ANSI/ALI A14 industrial/professional set, and the "Arabic numeral" ladder (2, 3) is the older non-ANSI consumer labeling used by some retail guides [S1][S2]. Second, Type IAA and Type IA are both called "Extra Heavy Duty" by ALI but are split by capacity; industrial buyers typically see IAA reserved for the heaviest rigging, tool hauling, and two-person tasks, while IA covers standard trades work [S1][S3].
How to Calculate Your Real Load Before You Pick a Class
Add four numbers: your body weight, the weight of clothing and PPE, the weight of tools and supplies you are carrying, and the weight of tools and supplies stored on the ladder [S1]. A 200 lb worker carrying a 30 lb tool belt and a 20 lb drill on a paint tray is loading the ladder with 250 lb before stepping on a rung, which means Type I is the floor, not Type II.
OSHA-compliant practice is straightforward: do not load ladders beyond their duty rating, follow manufacturer instructions, and inspect ladders regularly for defects before use [S3]. Skipping the PPE and tool weight in the sum is the single most common cause of an underrated ladder being put into service, and the failure mode is usually a rail kink or a rung shear, not a dramatic collapse [S1][S3]. For deeper background on the aluminum alloy grades used in side rails and rungs, the duty-rating number is set by the rail section, rung attachment, and the spreader or tie-rod, not by the alloy label alone.
Who Each Class Is For, and Who It Is Not For
Type IAA (375 lb) and Type IA (300 lb) are specified for industrial sites, construction, and high working heights where heavy tools, dual workers, or hoisted loads are routine [S3]. They are overkill, and not cost-effective, for a homeowner changing a porch light. Type I (250 lb) covers standard maintenance, repair, and light construction on commercial and industrial buildings, and is often the default industrial stepladder [S3][S4].
Type II (225 lb) and Type III (200 lb) are intended for household maintenance, occasional repair, and light improvement work, and are widely sold through retail channels as "homeowner" ladders [S3]. They are not appropriate for daily trades work, for workers carrying more than a hand tool, or for any environment where the load could spike with stored materials on the platform or tray. Choosing a lighter class to save cost on a job site is the textbook path to an OSHA violation and a workers' comp claim [S3].
Material Trade-Off: Why Aluminum, and When It Is the Wrong Choice
Ladders are built from one of three basic materials: wood, fiberglass, and metal (aluminum) [S1]. Aluminum is the lightest of the three for a given duty rating, which matters when a 24 ft extension ladder is being moved and set up multiple times a day. The trade-off is electrical conductivity: ALI states explicitly that if there are sources of electricity in the work area, a metal ladder should be rejected because the body can complete a circuit between the live source, the aluminum ladder, and ground, causing shock, fall, or cardiac arrest [S1].
For work near energized lines, panelboards, or any conductor, fiberglass is the correct material at the same duty class, not a lighter-class aluminum substitute. For purely mechanical work, painting, drywall, roofing, and warehouse tasks, aluminum at Type IA or Type I is the standard professional pick [S1][S3][S4]. Cross-reference material science on aluminum window door extrusions if you want to see how the same 6000-series alloys are formed for ladder rails versus architectural sections.
Comparing the Five Classes Side by Side
For an at-a-glance spec match, the five ANSI/ALI A14 classes line up against four decision criteria: maximum load (lb), typical use case, weight penalty vs the next class up, and acceptable environment. [S1]
Type IAA: 375 lb, industrial and rigging, heaviest in class, suitable only for non-electrical industrial sites [S1][S3]. Type IA: 300 lb, professional trades and construction, moderate weight, also non-electrical unless switched to fiberglass at the same class [S1][S3]. Type I: 250 lb, maintenance and light construction on commercial sites, the most common industrial stepladder, non-electrical preference [S3][S4]. Type II: 225 lb, household and light repair, lighter than Type I, retail and homeowner channels, non-electrical [S2][S3]. Type III: 200 lb, occasional household tasks only, lightest class, retail only, not for daily work [S2][S3].
The duty rating number, not the price tag or the step-count, is the binding constraint; if your real load is 240 lb you are buying Type I minimum, regardless of how attractive the Type II looks on the shelf [S1][S3].
Selection Workflow That Survives a Site Audit
Step one is the environment check: identify electrical hazards, ground conditions, and overhead obstructions, and that alone eliminates aluminum in favor of fiberglass on most energized work [S1]. Step two is the load sum: body weight plus clothing and PPE plus carried tools plus stored tools, with a 10 to 20 percent margin so a one-time load spike does not push you into the next class failure zone [S1][S3]. Step three is the length and configuration: stepladder for self-supporting work from 4 ft to 20 ft, straight ladder for non-self-supporting climbs from 4 ft to 30 ft, and platform ladder when standing at the top on a railed surface is required [S4].
Step four is the duty class pick from the table above. Step five is the inspection and labeling check: every compliant ladder carries a label stating the highest standing level, and ALI rules forbid standing on the top cap of a stepladder or the step below it, and forbid climbing the top three rungs of an extension ladder [S1]. On articulating-crane and heavy-rig sites, ladder selection often sits next to articulated crane truck folded boom transport height planning because the same access rules govern the boom approach and the ladder approach.
Standards, Compliance, and What an Auditor Will Check
The duty-rating system is published by ALI and aligns with the ANSI/ASC A14 committee standards, which is the document set OSHA references for ladder construction and use [S1]. OSHA compliance for duty ratings reduces to three verifiable items: do not load the ladder beyond its duty rating, follow manufacturer instructions, and inspect the ladder regularly for defects [S3].
On a job site, that translates into four physical artifacts an auditor will look for: the duty-rating label on the side rail, the highest-standing-level label, an inspection log or tag for daily checks, and storage that prevents rail warping and rung contamination. The ALI laddersafetytraining.org resources and the A14 standards documents are the canonical references a safety manager should keep on file [S1].
For a 2026 cross-reference on adjacent mobile-equipment safety standards used in the same facilities, the ANSI/ITSDF B56.1-2020 forklift safety standard covers a parallel set of OSHA cross-references for powered industrial trucks, and the duty-rating logic for ladders follows the same load-plus-environment-plus-inspection pattern. Track the next ANSI A14 committee meeting minutes for any revision to the 375/300/250/225/200 ladder, and watch for retailer labeling migration between the Roman-numeral and Arabic-numeral systems, which has been the most common source of consumer confusion in retail channels since 2022 [S1][S2].