Ladder Reach Calculator

Check ladder inputs

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Unit system:

Choose how height and load inputs are displayed.

Ladder job:

Pick the job that matches the height you are entering, then adjust the fields below.

{{ targetHeightLabel }}:

Rail extension above support:

Use the local requirement or ladder label; 3 ft is the common access minimum.

Standing reach allowance:

Use a conservative reach that does not require leaning sideways or standing above the permitted level.

Candidate ladder size:

The fit table compares common ladder sizes against the current job and safety assumptions.

Load preset:

Seed the duty-rating check from common carried-item scenarios.

Worker plus carried load:

Edit the exact combined load; the safety checks compare it against the selected duty rating.

Duty rating:

Select the ladder label rating for the load check.

Ladder material:

Use the material and electrical setting to flag high-risk setups.

Extension ladder top reserve: {{ topReserveDisplay }}

Default keeps about four feet of rail above the standing level for wall-work reach checks.

Stepladder top reserve: {{ stepReserveDisplay }}

Default reserves two feet below the nominal stepladder size before adding standing reach.

Work near energized electrical hazards

Enable this when the ladder, person, or carried materials could approach energized conductors or equipment.

Metric	Value	Use	Copy
{{ row.metric }}	{{ row.value }}	{{ row.use }}

Ladder size	Capacity in this mode	Fit	Margin	Copy
{{ row.size }}	{{ row.capacity }}	{{ row.fit }}	{{ row.margin }}

Check	Status	Detail	Copy
{{ row.check }}	{{ row.status }}	{{ row.detail }}

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Ladder reach is not the same as ladder length. A labeled 24 ft extension ladder does not provide 24 ft of vertical access because the ladder leans, overlap between sections reduces usable extension, and access work may require rails to continue above the support. A stepladder has a different limit because the top cap and upper steps are not ordinary standing levels.

Reach planning starts with the job. Accessing a roof or upper landing is a transition problem, so the ladder must reach the support and provide enough rail above it for a handhold. Working on a wall, window, gutter, shelf, ceiling, or fixture is a standing-level problem, so the required ladder size depends on safe standing height plus a realistic reach allowance.

The familiar 4-to-1 setup rule puts the base about one quarter of the working ladder length away from the wall or support. That geometry is roughly a 75.5 degree ladder angle. A steeper ladder can tip backward or be hard to climb safely, while a flatter ladder increases slip risk and loading on the ladder and support.

Load rating is separate from reach. The person, clothing, tools, carried material, and accessories all count against the ladder's duty rating. A ladder that reaches the work can still be the wrong ladder if the combined load is near or above the rating, the material is unsuitable near electrical hazards, or the support point is not strong and stable.

A calculator can organize the geometry and compare common ladder sizes, but it cannot inspect the ladder label, feet, locks, ground, weather, traffic, power lines, or local rules. Treat reach output as a planning check before choosing and setting up the real ladder.

How to Use This Tool:

Choose the job type first because roof access, extension-ladder wall work, and stepladder work use different reach assumptions.

Select US customary or metric input. Ladder sizes remain shown in feet because common extension and stepladder labels use foot sizes.
Choose the ladder job, then enter the target height. For roof access, measure to the roof edge or landing support. For wall or step work, measure the work point height.
For roof access, set the rail extension above support. For wall and stepladder work, set a conservative standing reach allowance that does not depend on leaning sideways.
Leave candidate size on auto to pick the smallest common size, or select a ladder you already own to check the fit margin.
Set worker plus carried load, duty rating, ladder material, and the electrical hazard switch. These do not change the height geometry, but they affect the safety checks.
Use Reach Sizing Table, Ladder Size Fit, Setup Safety Checks, Reach Clearance Chart, and JSON to compare the recommendation with candidate ladders and review assumptions.

Correct validation errors before using the result. Target height, standing reach allowance, and worker load must be positive, and advanced reserve values cannot be negative.

Interpreting Results:

The summary names the recommended ladder type and labeled size. The supporting line reports modeled reach capacity and margin, which is more useful than size alone because two ladders with the same label can differ by extension overlap, highest standing level, and manufacturer instructions.

Ladder Size Fit compares common sizes against the current job. A Short row does not meet the modeled target. A Tight row reaches with less than about 1 ft of margin. An Oversized row may reach, but it can be harder to transport, place, and handle.

Ladder reach result interpretation
Result	Read it as	What to verify on site
`Required rail length`	Modeled sloped length or stepladder size before choosing a common label size.	Check the actual ladder label for maximum extended length or highest standing level.
`Base setback`	Approximate horizontal distance from support to ladder foot for extension setups.	Confirm the ground is level, stable, clear, and protected from traffic.
`Duty load margin`	Selected rating minus worker plus carried load.	Include tools, materials, clothing, and accessories, not only body weight.
`Setup Safety Checks`	Angle, access extension, standing-level reserve, support, duty, electrical, and inspection notes.	Use these as reminders, not as permission to climb an unsafe ladder.

The electrical warning is intentionally conservative. Metal ladders should not be used near energized electrical hazards, and nonconductive ladder choices still require clearance, site control, and inspection.

Technical Details:

Extension-ladder reach uses right-triangle geometry. The ladder rail is the hypotenuse, the wall or support height is the vertical leg, and the base setback is the horizontal leg. With a 75.5 degree angle, vertical height is the sloped rail length multiplied by the sine of the angle, while base setback is the sloped rail length multiplied by the cosine of the angle.

Stepladder reach is not angle-based in this model. The nominal stepladder size is reduced by a top reserve, then a standing reach allowance is added. That keeps the top cap and upper step out of the usable standing area and avoids treating maximum human reach as a stable work posture.

Formula Core:

The equations below use feet internally. Metric input is converted to feet before calculation and shown back with metric display values.

\begin{array}{lcl} θ & = & 75.5 ° \\ L_{support} & = & \frac{H_{support}}{\sin (θ)} \\ D_{base} & = & L_{support} \times \cos (θ) \\ L_{access} & = & L_{support} + E_{rail} \\ L_{work} & = & \frac{H_{target} - R_{standing}}{\sin (θ)} + R_{top} \\ S_{step} & = & H_{target} - R_{standing} + R_{stepTop} \end{array}

For an 18 ft roof edge with a 3 ft rail extension, the sloped rail needed to the support is about 18.6 ft. Adding the 3 ft extension gives about 21.6 ft required rail, so the smallest common extension ladder in the tool's size table that can satisfy the modeled maximum extension is 24 ft.

Ladder reach calculation modes and boundaries
Mode	Core rule	Boundary
Roof or landing access	Support height is divided by sine of 75.5 degrees, then rail extension above support is added.	The result is compared with common extension ladder maximum extended lengths.
Lean to support	Support height is divided by sine of 75.5 degrees with no access extension added.	The support must be suitable for the ladder and the job.
Extension wall work	Standing reach is subtracted from target height, then a top rail reserve is added.	Standing on upper rungs is not treated as usable reach.
Stepladder work	Standing reach is added after reserving distance below the top cap.	Do not use the top cap or top step unless the ladder is specifically designed for it.
Duty rating	Load margin equals selected duty rating minus worker plus carried load.	Negative margin means the modeled load exceeds the selected rating.

Common-size tables are planning approximations. Manufacturer ladder labels, maximum extended length, overlap, duty rating, permitted standing levels, stabilizer accessories, and local safety rules take priority over a generic reach model.

Limitations and Safety Notes:

This page cannot decide whether a ladder can be used safely at a real site. It does not inspect the ladder, confirm duty labels, measure slope or ground firmness, test support strength, identify power lines, account for wind, or determine whether fall protection, scaffolding, lift equipment, or a second person is required.

Use the result for early sizing, rental planning, or checking whether an existing ladder is likely to be short. Before climbing, follow the ladder label, employer policy, OSHA requirements, local rules, and the manufacturer's instructions.

Worked Examples:

Roof access at 18 ft

An 18 ft roof edge with 3 ft of rail extension needs more than 21 ft of modeled rail length. The recommendation moves to a common 24 ft extension ladder, and the setup check reports the base setback for the support height.

Wall work at 24 ft

For a 24 ft work point with a 6.5 ft standing reach allowance and a 4 ft top reserve, the vertical standing target is 17.5 ft before angle geometry. The extension size must leave enough rail above the modeled standing level, not merely touch the wall at 24 ft.

Stepladder work at 10 ft

A 10 ft ceiling task with a 6.5 ft reach allowance and 2 ft step-top reserve has a modeled stepladder size need of 5.5 ft. The common-size comparison helps decide whether a 6 ft stepladder is enough or whether a larger ladder gives a more comfortable margin.

FAQ:

Why does a 20 ft extension ladder not reach 20 ft vertically?

The ladder is angled, and extension ladders have section overlap. The modeled vertical reach uses maximum extended length and the 75.5 degree setup angle, not the nominal label alone.

Can I use this for metric planning?

Yes. Metric height and load inputs are converted internally, while ladder labels remain in feet because common extension and stepladder sizes are sold that way.

Why does material affect warnings but not ladder size?

Fiberglass, aluminum, and wood do not change the triangle geometry. Material matters for electrical and handling risk, so it appears in the setup checks instead.

Does the calculator approve a ladder for use?

No. It estimates size and margin from entered assumptions. The ladder label, condition, site hazards, user training, and applicable safety rules decide whether it can be used.