Calculate air draft and actual bridge clearance accounting for vessel trim and tidal state.
Vessel Dimensions
Drafts
Mast / Highest Point Location
Bridge clearances are charted relative to a high-water datum; water levels are measured from a low-water datum. Enter the appropriate values for your region.
| Region | Bridge Datum (High Water) | Tide Datum (Low Water) |
|---|---|---|
| USA (Coastal) | MHW — Mean High Water | MLLW — Mean Lower Low Water |
| UK / Europe | HAT — Highest Astronomical Tide | LAT — Lowest Astronomical Tide |
| Great Lakes | LWD — Low Water Datum | IGLD 85 — Fixed Elevation |
| Panama Canal | Max Lake Level | PLD — Precise Level Datum |
Negative water levels (below chart datum) are valid. Example: a −2.0 ft tide means the water is 2.0 ft below datum — the calculator adds this to your clearance automatically.