Fork extension length calculator
Maximum fork extension length: max_extension_length = fork_length x 1.5 (trucks up to 5,000 kg) or fork_length x 1.4 (trucks over 5,000 kg). Enter your numbers below; the formula and its source are shown under the result.
The capacity shown is an upper bound before the extensions' own weight. Fitting extensions can change the truck's rating: check with the truck maker or dealer.
The formulas
max_extension_length = fork_length x 1.5 (trucks up to 5,000 kg) or fork_length x 1.4 (trucks over 5,000 kg)
Supralift: the extension must not be more than 50% longer than the original forks (40% for trucks over 5,000 kg), the load carried should not overhang the extension, and residual capacity is reduced with extensions fitted. Turning 50% / 40% into 1.5 / 1.4 is our arithmetic.
Worked example: Our arithmetic: 48 in forks -> extension no longer than 72 in (up to 5,000 kg) or 67.2 in (over 5,000 kg).
[src]max_load_moment = rated_capacity × rated_load_center; revised_capacity = max_load_moment / new_load_center
Same math as OSHA's field calculation, expressed as load moment. Raymond West: assumes uniform, centered loads; non-uniform loads reduce capacity more than calculated. Does not account for the attachment's own weight; OSHA 1910.178(a)(4)-(5) requires manufacturer approval and a revised plate for capacity-affecting changes.
Worked example: Raymond West: 5,000 lb x 24 in = 120,000 in-lb; with 60 in forks the load center becomes 30 in, so 120,000 / 30 = 4,000 lb.
[src]Estimate only. The capacity on the machine's data plate is the legal limit; never exceed it.
Sources
- Fork Extensions (Supralift materials handling glossary) (retrieved November 6, 2026)
- How To Determine Your Forklift Capacity When Adding New Attachments (Raymond West) (retrieved November 4, 2026)