Four up.
One out.

The direct answer

The 4-to-1 ladder rule means the base of a non-self-supporting ladder sits approximately 1 foot away from the upper support for every 4 feet of working ladder length. OSHA's construction standard defines that working length as the distance along the ladder between its feet and the top support. Divide that measured rail distance by four to estimate the horizontal setback.

For example, if there are 16 feet of ladder rail between the feet and the wall contact, start with the feet about 4 feet from the wall. At 20 feet of working length, use about 5 feet. The resulting angle is close to 75.5 degrees from level ground—the extension-ladder pitch described by the American Ladder Institute and the approximately 75-degree angle recommended by NIOSH.

The ratio is a setup rule, not a ladder-size formula. It does not account for section overlap, the highest standing rung, working reach, or the extra rail needed above an upper landing. Choose the correct ladder length first, then set that ladder at its permitted angle. The ladder-size guide explains those different measurements.

Use the right “four” in the calculation

Two versions of the rule appear in safety material. OSHA's construction language and ALI's extension-ladder guidance use working length along the ladder. Werner's current plain-language FAQ describes vertical height to the support point. Both are useful field explanations, but they are not mathematically identical.

At a 16-foot vertical support height, the simple height-divided-by-four shortcut gives 4 feet. Geometry at 75.5 degrees puts the base about 4 feet 1½ inches out. That small difference explains why the field shortcut is described as approximate. Do not split inches while ignoring a soft foot, uneven rail support, a damaged shoe, or the manufacturer's own setup indicator.

Also do not divide the number printed largest on the ladder. A nominal 20-foot extension ladder may have less maximum working length because its sections overlap. “Maximum reach” may add an assumed person's reach. Measure or verify the actual distance from the feet to the upper support in the final extended configuration.

Set the angle in five checks

1. Choose the foot location. Start on firm, level, clean ground, clear of doors, vehicles, people, window wells, loose landscaping, and electrical hazards.
2. Choose a solid upper support. Both rails need equal support unless the exact ladder uses an approved single-support attachment. Do not assume glass, a gutter, loose trim, or a movable surface can carry the setup.
3. Pre-plan the setback. For a quick space check, divide the vertical support height by four. If a 20-foot-high contact point is planned, reserve roughly 5 feet of horizontal ground.
4. Raise and extend while unoccupied. Follow the model's instructions, preserve required section overlap, engage both rung locks, and never shift or extend the ladder with anyone on it.
5. Verify the final setup. Check the working length, calculate the approximate quarter-length setback, confirm the angle, inspect both feet and top contacts, then secure or barricade the ladder where displacement is possible.

The familiar arm test—stand with toes at the feet and reach forward toward a rung near shoulder height—is only a rough field check. Body proportions vary. A label, manufacturer-provided indicator, or suitable angle tool is the better control. NIOSH's current Ladder Safety App page describes a visual, sound, and vibration angle tool, but also warns that the app is not currently receiving updates. Treat it as a secondary check, not a replacement for the current ladder instructions.

Roof access adds a separate three-foot question

When a portable ladder is used for access to an upper landing in covered construction work, OSHA says the side rails must extend at least 3 feet above that landing, or the specified securing and grasping alternative must be used when the ladder cannot extend that far. That portion above the roof does not move the upper support point used in the angle measurement. It does, however, require additional ladder length, proper overlap, and a controlled transition.

Use the one-story gutter guide or two-story house guide to choose the length category before treating the 4-to-1 ratio as the final answer.

Too steep and too shallow fail differently

Too steep: the feet are too close

A steep ladder can tip backward or pull away from its upper support as the user climbs. It also changes the climber's balance and may tempt someone to stand higher to recover reach. Do not move the feet toward the wall to make an undersized ladder touch the job. Choose the correct length or a different access method.

Too shallow: the feet are too far out

A shallow ladder increases the tendency for the base to slide away and changes the forces carried by the rails and support. NIOSH identifies incorrect setup angle as a major cause of extension-ladder incidents and reports that base slide-out from incorrect angle appears in about 40% of the ladder-related injuries summarized in its guidance.

Slip-resistant feet are not permission to use a slippery surface or the wrong angle. OSHA requires stable, level support unless the ladder is secured or stabilized, and calls for securing or barricading ladders exposed to traffic or other displacement. Securing a ladder addresses movement; it does not turn a visibly bad pitch, weak top contact, or unsuitable ladder into a good setup.

Where 4-to-1 applies—and where it does not

Never close a normal stepladder and lean it against a wall unless its label explicitly permits a leaning configuration. Never assume a multi-position model may be used in every shape it can physically make. The designed and labeled mode comes first; the angle rule applies only after the ladder is in an approved non-self-supporting mode.

Two extension-ladder paths after the math fits

The Werner D6220-2 is a current 20-foot, Type IA fiberglass example with a published 17-foot maximum working length. The Xtend+Climb 785P+ is a current 15.6-foot aluminum telescoping example with a published 12.5-foot safe working height, 36-inch closed height, and Type I rating. Those figures are not interchangeable with support height or angle. If either model cannot fit the measured support, setback, load, storage, electrical environment, and instructions, it is the wrong path.

The before-you-climb checklist

1. Confirm the ladder is designed and labeled for a non-self-supporting configuration.
2. Inspect rails, rungs, feet, rope, pulley, locks, labels, and hardware.
3. Choose firm, level footing and solid, equal support for both upper rails.
4. Measure the actual working length from the feet to the top support.
5. Divide that working length by four for the approximate base setback.
6. Verify about a 75-degree angle with the label, indicator, or appropriate tool.
7. Preserve required overlap and stay below the marked highest standing level.
8. Add rail length and transition planning when accessing an upper landing.
9. Secure or barricade against displacement without using that as an excuse for a bad angle.
10. Descend before moving, shifting, or extending the ladder.

Bottom line: use 4-to-1 as a measured setup check, not a slogan. For every 4 feet of working ladder length between the feet and upper support, place the base about 1 foot out, then confirm the resulting pitch near 75 degrees. If the base has no level place to sit, the top cannot support both rails, or correct angle makes the ladder too short, change the ladder or the access method rather than changing the rule.

Sources checked September 5, 2026: OSHA 29 CFR 1926.1053 for the quarter-working-length definition, upper-landing rail extension, stable surfaces, displacement, locks, and movement; current NIOSH ladder-safety guidance and Ladder Safety App information for approximately 75-degree setup, angle risk, and the app's current update notice; the American Ladder Institute's extension-ladder guidance for the 75½-degree pitch, quarter-rail-length rule, support, and inspection; Werner's current 4-foot-rule explanation; and current manufacturer information for the Werner D6220-2 and Xtend+Climb 785P+. Cool Ladder has not hands-on tested these models. This is practical education, not jobsite training or legal advice; current manufacturer instructions and applicable rules control.