Ladder Reach Calculator

Ladder job:

Choose the job before entering the vertical height you measured.

{{ targetHeightLabel }}:

Rail extension above landing:

Standing reach allowance:

Rail above highest standing level:

Reserve below top cap:

Candidate ladder:

Load starting point:

Person plus carried load:

Printed duty rating:

Ladder material:

Work could approach energized conductors or equipment:

Turn this option on when work could approach energized conductors or equipment is required.

If this may apply, stop and follow the required electrical-clearance and qualified-person rules before choosing equipment.

Extra planning buffer:

The neutral default is 0; a buffer is a planning preference, not a substitute for the ladder label.

Display precision:

One decimal place is the neutral presentation default.

Measure	Value	Basis	Copy
{{ row.label }}	{{ row.value }}	{{ row.note }}

Ladder size	Modeled capacity	Margin	Fit	Copy
{{ row.size }}	{{ row.capacity }}	{{ row.margin }}	{{ row.fit }}

Check	Status	Action	Copy
{{ row.check }}	{{ row.status }}	{{ row.action }}

A ladder that reaches a roof edge is not automatically long enough for safe access, and a ladder long enough on the ground may not provide a permitted standing level for work. The job decides which height matters. Roof access needs rail above the landing, supported extension-ladder work depends on the contact point, wall work must leave unused rail above the highest standing level, and stepladder work must keep the user below the top cap and prohibited steps.

Extension ladders trade vertical reach for stability. Leaning the rails at about 75.5 degrees means only part of their working length becomes height; the rest becomes the horizontal distance from the wall or support. A ladder set too upright can tip backward, while one set too shallow can slide or carry loads differently from its intended setup. Uneven ground, weak support, doors, traffic, weather, and the need to lean sideways can make an otherwise adequate length unsuitable.

Nominal size: The length printed for the ladder. An extension ladder's usable extended length is shorter because sections overlap.
Modeled capacity: The highest target the selected size reaches under the chosen job geometry and standing restrictions.
Duty rating: The total rated load, including the person, clothing, protective equipment, tools, supplies, and anything carried or placed on the ladder.

Length and duty rating solve different problems. Extra reach does not create extra load capacity, and a higher duty rating does not make a short ladder reach farther. Material is another separate decision. Where a person or ladder could contact exposed energized equipment, workplace rules require nonconductive side rails; even a fiberglass ladder does not remove the need for electrical clearance and qualified safety planning.

A calculated size is a planning starting point, not permission to climb. Confirm the actual ladder label, highest standing level, extension overlap, condition, footing, support, access method, and rules that apply to the site. If the target is beyond the listed size range or the work cannot be performed without overreaching, use another access method rather than forcing the ladder to fit.

How to Use This Tool:

Start with the job and the vertical height measured from level ground or floor. The same height can require a different ladder when it is an access point rather than a work point.

Choose the Ladder job and enter the requested target height. For roof access, measure to the landing or roof edge; enter the required rail extension separately.
Set the standing allowance or upper reserve shown for wall or stepladder work. Use a reach that does not depend on tiptoeing or sideways overreach, and confirm the permitted standing level on the ladder label.
Enter Person plus carried load and choose the Printed duty rating. Replace any load preset with the real combined weight. Mark the electrical-hazard option whenever energized conductors or equipment could be approached.
Review Recommended size, Selected margin, Base setback, and Setup checks. A negative margin, an over-rating warning, less than 3 ft of rail extension for upper-landing access, or an electrical warning must be resolved before relying on the plan.

Interpreting Results:

The recommended size is the smallest listed nominal size whose modeled capacity reaches the adjusted target. Compare it with the ladder you actually have. A positive margin is extra modeled reach, not permission to stand higher, change the setup angle, or work beyond the label.

Short means the selected capacity is below the target. Choose a longer listed size or another access method.
Tight means the remaining modeled reach is less than 1 ft. Recheck measurements and site conditions before choosing equipment.
Oversized means a non-short ladder is more than 8 ft above the recommended extension-ladder size, or more than 4 ft above the recommended stepladder size. Excess length can be awkward even when reach is adequate.
Near rating leaves less than 25 lb between combined load and the printed duty rating. Use the actual total load rather than a preset.

Technical Details:

Reach is modeled in feet at a fixed 75.5-degree extension-ladder angle. Measurements entered in metres are converted with 1 m = 3.280839895 ft, and kilograms are converted with 1 kg = 2.204622622 lb. Full precision is retained; the one- or two-decimal choice changes presentation only.

Formula Core:

For upper-landing access, the required rail length combines the sloped length needed to reach support height with the rail extension above the landing.

L_{r} = \frac{H_{a}}{\sin (75.5 °)} + E

Here, H_a is target height plus any planning buffer, E is rail extension above the landing, and L_r is the required rail length. The base setback for a supported extension ladder is:

B = \frac{H_{s}}{\sin (75.5 °)} \times \cos (75.5 °)

For extension-ladder wall work, modeled capacity is working length minus the reserved upper rail, projected vertically, plus standing reach. Stepladder capacity uses its nominal height minus the top-cap reserve plus standing reach.

\begin{matrix} C_{wall} & = & (L - R_{rail}) \sin (75.5 °) + S \\ C_{step} & = & L - R_{cap} + S \end{matrix}

Lookup Core:

Extension-ladder recommendations use the following nominal-size and maximum-extended-length pairs. The capacity formula then applies the selected job geometry to the maximum extended length.

Listed extension ladder sizes and maximum extended lengths
Nominal size	Maximum extended length
16 ft	13 ft
20 ft	17 ft
24 ft	21 ft
28 ft	25 ft
32 ft	29 ft
36 ft	32 ft
40 ft	35 ft
44 ft	39 ft
48 ft	43 ft
60 ft	48 ft

Stepladder selection checks nominal sizes of 4, 5, 6, 7, 8, 10, 12, 14, 16, 18, and 20 ft. If no listed size reaches the target, the result is marked beyond the listed range rather than extrapolating a larger ladder.

Rule Core:

The reach, load, access, and electrical checks are independent. Passing one does not cancel a failure in another.

Ladder planning rule boundaries
Check	Exact rule	Meaning
Reach margin	Margin < 0 ft	Short
Reach margin	0 ft ≤ margin < 1 ft	Tight
Load margin	Rating − combined load < 0 lb	Over rating
Load margin	0 lb ≤ margin < 25 lb	Near rating
Upper landing	Rail extension < 3 ft	Below the modeled OSHA access threshold
Electrical	Hazard marked and material is aluminum	Conductive-material warning

For an 18 ft upper landing with 3 ft of rail extension, the required rail length is about 21.59 ft. A listed 28 ft ladder has a 25 ft maximum extended length and a modeled landing capacity of about 21.30 ft, leaving about 3.30 ft of vertical reach margin. Its base setback is about 4.66 ft. These figures are geometry and lookup results, not a field approval.

Limitations and Safety Notes:

The model assumes level geometry and a fixed setup angle. It does not inspect the ladder, verify the manufacturer's working-length chart, account for flexible surfaces or side loading, evaluate fall protection, or decide whether a ladder is the right access system.

Use the ladder only for its designed purpose and never exceed its rated capacity.
Keep the top and bottom clear, secure or barricade the ladder where traffic could displace it, and withdraw damaged ladders from service.
Do not use the top or top step of a stepladder as a step. Follow the actual highest-standing-level marking.
For electrical exposure, follow applicable clearance and qualified-person rules. A material warning is not an electrical risk assessment.

References:

29 CFR 1926.1053 — Ladders, Occupational Safety and Health Administration.
Ladder Safety, National Institute for Occupational Safety and Health, January 23, 2024.