Crane load charts: don't trust a US ton rating against a metric tonne chart
A rigging plan for imported equipment listed crane capacity in tonnes, and the site's crane load chart was rated in US tons — reconciling the two before a lift, not during one, was the only responsible option.
We write the way we argue on the bench: exact factor, one sharp trap, one worked example you can re-check.
A rigging plan for imported equipment listed crane capacity in tonnes, and the site's crane load chart was rated in US tons — reconciling the two before a lift, not during one, was the only responsible option.
The factor below is the one that ends the argument — write it once, then stop improvising mid-job.
The factor that settles arguments
This is the relationship our converters use. Screenshot it if you have to — just stop re-deriving it from a half-remembered blog post.
1 US ton = 0.907185 tonne
Write that line once at the top of your notes. Every later arithmetic step should point back to it instead of inventing a friendlier number mid-stream.
The mistake that keeps showing up
Assuming a crane's US ton rating and a required tonne rating are interchangeable numbers, when a metric tonne is roughly 10% heavier — a chart that's 'close enough' on paper can be a real safety margin loss in practice.
I still write the unit next to every intermediate value. It looks pedantic until it catches the one swap that would have shipped wrong.
- Write down the known value in US tons (load chart).
- Confirm the target unit is really tonnes, not a similar-looking one.
- Apply the factor: 1 US ton = 0.907185 tonne.
- Round only at the end, to the precision your tool or spec supports.
Worked example
A lift plan specifies a load of 50 tonnes, and the available crane's chart is rated in US tons.
50 US tons (load chart) × 0.907185 = 45.3593 tonnes
That's 45.3593 tonnes — round only to the precision your tool or spec actually needs.
Flip the factor once as a sanity check. If you do not land near the starting number, you mixed definitions or inverted the direction.
Quick reference table
| US tons (load chart) | Calculation | tonnes |
|---|---|---|
| 1 | 1 × 0.907185 | 0.907185 |
| 2 | 2 × 0.907185 | 1.81437 |
| 5 | 5 × 0.907185 | 4.53592 |
| 10 | 10 × 0.907185 | 9.07185 |
Use the table for speed once you trust the factor. Do not use it as a substitute for understanding which definition of the unit you are on.
Why the exact number matters
Crane load capacity has almost no margin for casual rounding — misjudging the unit difference on a heavy lift is a direct safety hazard, not just a paperwork issue.
Precision is not about showing off decimals. It is about making sure the shopping list, the machine setting, and the acceptance check are all describing the same physical quantity.
Pocket recap
Multiply US tons by 0.907 to get tonnes, and always confirm which unit a load chart actually uses before rigging a heavy lift.
Keep the converter link nearby for the next time the same debate shows up in a group chat. Re-typing the factor from memory is how the wrong cousin of a unit sneaks back in.
Try the converters mentioned in this article
FAQ
What is the exact US tons (load chart) to tonnes factor here?+
1 US ton = 0.907185 tonne
Should I round partway through the calculation?+
No — carry full precision through the multiplication and round only the final answer, to the precision your tool, gauge, or spec actually supports.
What's the single biggest mistake people make with this conversion?+
Assuming a crane's US ton rating and a required tonne rating are interchangeable numbers, when a metric tonne is roughly 10% heavier — a chart that's 'close enough' on paper can be a real safety margin loss in practice.
This article was written by The Turbo Unit Converter engineering desk (Applied units & field metrology) and last reviewed on 2026-07-26 against NIST SP 811 and the BIPM SI Brochure. Read our full editorial policy.