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DepotOps report: US Federal Bridge Formula
Made 29 Sept 2026, 5:53 pm at depotops.com.au/bridge-formula. An estimate from the figures entered, not a weighbridge certificate, permit or legal advice.
Enter the number of axles and the distance between the outer ones to get the legal maximum under 23 CFR 658.17, or print a table for the lengths you run.
Rules checked 25 Sept 2026 against 23 CFR 658.17 (US Federal Bridge Formula). Official pages are watched weekly for changes.
L is the distance in feet between the outer axles of any group of two or more consecutive axles. Check every group — tandems, the tractor, the trailer and the whole combination — not just the outer bridge.
Maximum on this group
Legal80,000 lb
W = 500 × (51×5/(5−1) + 12×5 + 36) = 79,875.0 → 80,000 lb
0 lb of margin.
| L (ft) | 2 axles | 3 axles | 4 axles | 5 axles | 6 axles | 7 axles | 8 axles | 9 axles |
|---|---|---|---|---|---|---|---|---|
| 36 | 66,000 | 63,000 | 66,000 | 70,500 | 75,500 | 81,000 | 86,500 | 92,500 |
| 37 | 67,000 | 64,000 | 66,500 | 71,000 | 76,000 | 81,500 | 87,000 | 93,000 |
| 38 | 68,000 | 64,500 | 67,500 | 72,000 | 77,000 | 82,000 | 87,500 | 93,500 |
| 39 | 69,000 | 65,500 | 68,000 | 72,500 | 77,500 | 83,000 | 88,500 | 94,000 |
| 40 | 70,000 | 66,000 | 68,500 | 73,000 | 78,000 | 83,500 | 89,000 | 94,500 |
| 41 | 71,000 | 67,000 | 69,500 | 73,500 | 78,500 | 84,000 | 89,500 | 95,000 |
| 42 | 72,000 | 67,500 | 70,000 | 74,500 | 79,000 | 84,500 | 90,000 | 95,500 |
| 43 | 73,000 | 68,500 | 70,500 | 75,000 | 80,000 | 85,000 | 90,500 | 96,000 |
| 44 | 74,000 | 69,000 | 71,500 | 75,500 | 80,500 | 85,500 | 91,000 | 97,000 |
| 45 | 75,000 | 70,000 | 72,000 | 76,000 | 81,000 | 86,500 | 91,500 | 97,500 |
| 46 | 76,000 | 70,500 | 72,500 | 77,000 | 81,500 | 87,000 | 92,500 | 98,000 |
| 47 | 77,000 | 71,500 | 73,500 | 77,500 | 82,000 | 87,500 | 93,000 | 98,500 |
| 48 | 78,000 | 72,000 | 74,000 | 78,000 | 83,000 | 88,000 | 93,500 | 99,000 |
| 49 | 79,000 | 73,000 | 74,500 | 78,500 | 83,500 | 88,500 | 94,000 | 99,500 |
| 50 | 80,000 | 73,500 | 75,500 | 79,500 | 84,000 | 89,000 | 94,500 | 100,000 |
| 51 | 81,000 | 74,500 | 76,000 | 80,000 | 84,500 | 90,000 | 95,000 | 100,500 |
| 52 | 82,000 | 75,000 | 76,500 | 80,500 | 85,000 | 90,500 | 95,500 | 101,500 |
| 53 | 83,000 | 76,000 | 77,500 | 81,000 | 86,000 | 91,000 | 96,500 | 102,000 |
| 54 | 84,000 | 76,500 | 78,000 | 82,000 | 86,500 | 91,500 | 97,000 | 102,500 |
| 55 | 85,000 | 77,500 | 78,500 | 82,500 | 87,000 | 92,000 | 97,500 | 103,000 |
| 56 | 86,000 | 78,000 | 79,500 | 83,000 | 87,500 | 92,500 | 98,000 | 103,500 |
| 57 | 87,000 | 79,000 | 80,000 | 83,500 | 88,000 | 93,500 | 98,500 | 104,000 |
| 58 | 88,000 | 79,500 | 80,500 | 84,500 | 89,000 | 94,000 | 99,000 | 104,500 |
| 59 | 89,000 | 80,500 | 81,500 | 85,000 | 89,500 | 94,500 | 99,500 | 105,000 |
| 60 | 90,000 | 81,000 | 82,000 | 85,500 | 90,000 | 95,000 | 100,500 | 106,000 |
Struck-through values are formula results that another limit overrides: the 80,000 lb Interstate gross limit, 20,000 lb per single axle, or 34,000 lb for a tandem (40–96 in spread).