Ladder Angle Calculator — find the safest ladder angle

Use this Ladder Angle Calculator to quickly find the safest ladder angle using the 4:1 rule. Enter two values (height, base distance, ladder length, or angle) and the tool will compute the rest. Ideal ladder angle is about 75° — for every 4 units of height, place the base 1 unit away.

Calculator

Vertical distance from ground to contact point

Horizontal distance from wall to ladder base

Actual length of the ladder (hypotenuse)

Angle between ladder and ground (toggle to radians)

α R B L
Angle: 75.0°

Results

Ladder Angle
75.0° Ideal (4:1 rule)
Ladder Length
–
Ladder Reach
–
Base Distance
–
Safe angle: 75° — 4:1 rule recommended.

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Ladder Safety & The 4:1 Rule

The 4-to-1 rule is a fundamental ladder safety principle: for every 4 units of height, move the ladder base 1 unit away from the wall. This creates an ideal angle of approximately 75 degrees.

Safety Checklist

  • Check ladder condition before use
  • Ensure stable, level footing
  • Maintain three points of contact
  • Don’t exceed weight capacity
  • Use the 4:1 angle rule
  • Extend ladder 3 feet above roof line
Ideal: 72°–78° (green) — Perfect 4:1 ratio
Caution: 70°–72° or 78°–80° (yellow) — Adjust if possible
Danger: <70° or >80° (red) — Move ladder base immediately

Calculation Examples

Metric Example

If you need to reach 4 meters high:

Base = Height / 4 = 4 m / 4 = 1 m
Angle = atan(4 / 1) = atan(4) ≈ 75.96°

Set ladder base 1 meter from wall for safe 75.96° angle.

Imperial Example

If you need to reach 20 feet high:

Base = Height / 4 = 20 ft / 4 = 5 ft
Angle = atan(20 / 5) = atan(4) ≈ 75.96°

Set ladder base 5 feet from wall for safe 75.96° angle.

Frequently Asked Questions

What is the safest ladder angle?
Aim for about 75° (the 4:1 rule) — for every 4 units of vertical height, move the ladder base 1 unit away from the wall.
How do I calculate the ladder angle?
Use the formula α = arctan(height / base). This tool calculates that automatically for you.
Can I calculate ladder length from angle?
Yes — if you know angle and either base or height, you can compute the ladder length using L = sqrt(R² + B²) or L = R/sin(α).
What is the OSHA 4-to-1 rule?
OSHA’s 4:1 rule states that for every 4 feet of ladder height, the base should be 1 foot away from the wall, creating a safe ~75° angle.
How do I measure ladder angle without a tool?
Use the ‘stand and reach’ test: Stand with toes at ladder base and extend arms — your hands should just reach the ladder rungs at shoulder height.

Ladder Safety Card

4:1 Rule: For every 4 units up, move base 1 unit out

Ideal Angle: 75° (72°-78° range)

Formula: Angle = arctan(Height / Base)

Safety Checklist

  • Inspect ladder before use
  • Ensure stable, level footing
  • Maintain three points of contact
  • Don’t exceed weight capacity
  • Use the 4:1 angle rule
  • Extend ladder 3 feet above roof line

CalculatorCave.com — Ladder Angle Calculator