Forklift clearance height refers to the minimum vertical space required for a forklift to safely pass under doorways, overhead fixtures, mezzanines, or inside trailers without striking any obstructions. It is determined by the Overall Lowered Height (OALH)—the height of the forklift when the mast is fully lowered. This is the most critical measurement for facility planning, as the OALH must be less than every doorway and overhead obstruction the forklift will encounter.
Typical Clearance Heights by Forklift Type
Forklift Type Lowered Height (OALH) Width Notes
Standard Warehouse Forklift 7'–8' (2.1–2.4 m) ~4' (1.2 m) Most common counterbalance models; 85–90 inches (7.0–7.5 ft)
Narrow Aisle Forklift 6'–7' (1.8–2.1 m) 36"–42" (3'–3.5') Lower profile for tight warehouses
Rough Terrain Forklift 8'–10' (2.4–3.0 m) Up to 7' (2.1 m) Taller due to larger tires and ground clearance
3-Stage (Triplex) Mast Diesel 84–85 inches (2.13–2.16 m) Max 45.7 inches (1.16 m) Example: 5,000 lb diesel forklift
Typical Mast Heights by Mast Type:
2-Stage Mast (Duplex): Lowered height around 85–90 inches
3-Stage Mast (Triplex): Lowered height similar to duplex when fully collapsed, but extends higher
Mast height typically ranges from 2.5 to 3.0 meters (8.2–9.8 ft) when fully lowered
Key Measurements to Know
Measurement Abbreviation Definition When to Use
Overall Lowered Height OALH Height from floor to highest fixed point with mast fully lowered Doorways, trailers, mezzanines, overhead fixtures
Overall Raised Height OARH Height with mast fully extended to maximum lift Racking height, ceiling clearance during lifting
Free Fork Height FFH Height forks can rise before mast extends Trailer loading without exceeding overhead clearance
Maximum Fork Height MFH Maximum height forks can reach Maximum racking height
Overhead Guard Height (OGH): On some forklifts, the overhead guard may be the highest point. Example: max OGH not to exceed 85 inches on a 5,000 lb diesel model.
Safety Clearance Requirements
Requirement Specification Source
Minimum overhead clearance (OSHA) Mast must clear all overhead obstructions at both lowest and highest positions
Canada OHS Regulation At least 150 mm (5.9 inches) above the highest point of the forklift or its load
General industry safety gap 5–6 inches (12.7–15.2 cm) above the highest point
Minimum torso clearance 39 inches from seat top to underside of overhead guard
Stand-up truck clearance At least 1,880 mm (74 inches) from platform to underside of overhead guard
Aisle side clearance Minimum 2 inches total (1 inch per side); .39 inches with centering wheels
How to Measure Clearance Height
Position the forklift on level concrete with forks fully lowered
Set mast to normal travel posture—close to vertical with slight rear tilt
Identify the true highest fixed point—this may be the mast top, overhead guard, lights, or attachments
Measure from floor to highest point using a tape measure or laser distance meter
Measure the door/opening from floor to the lowest obstruction (door track, drum housing, sprinkler pipe)
Add safety margin—at least 5–6 inches (12.7–15.2 cm) above the measured height
Critical Note: A forklift that clears a door with a bare mast may hit it with an attachment, load backrest, or work light installed. Always measure in the actual configuration the forklift will use.
Common Clearance Challenges
Trailer Loading: A standard semi-trailer has approximately 8 feet (2.44 m) of interior height. If the forklift's OALH is 8 feet and the free fork height is insufficient to reach double-stacked pallets, extending the mast can puncture the trailer roof.
Doorway Clearance: Most contact occurs at edges—door tracks, roll-up drums, or sprinkler pipes. Always measure the clear opening, not the nominal door size.
Low Ceilings: Forklifts with 3-stage masts may have similar lowered heights to 2-stage masts but require more clearance when raised.
Summary
Forklift clearance height is determined by the Overall Lowered Height (OALH)—the height from floor to the highest fixed point with the mast fully lowered. Typical OALH ranges from 6'–7' for narrow aisle forklifts to 8'–10' for rough terrain models, with standard warehouse forklifts averaging 7'–8' (85–90 inches). Safety regulations require at least 5–6 inches (12.7–15.2 cm) of clearance above the highest point of the forklift or load, with Canada OHS mandating 150 mm (5.9 inches). Always measure the forklift in its actual operating configuration—including attachments, lights, and backrests—and measure door openings at the lowest obstruction point, not the nominal door size.