Chart datum & ordnance datum

Differences at selected UK and Irish ports

Tidal levels are quoted relative to chart datum (approximately the lowest level due to astronomical effects and excluding meteorological effects). The heights of chart datum (CD) relative to ordnance datum (OD, at Newlyn) in the UK are listed below.

If for example, you have a data value for Liverpool of 1m relative to CD and want to convert it to be relative to OD, then this would be −3.93m, i.e., 1m + (−4.93m).

England – South

 

Avonmouth

−6.50m

Bournemouth

−1.40m

Devonport

−3.22m

Dover

−3.67m

Hinkley

−5.90m

Ilfracombe

−4.80m

Newhaven

−3.52m

Newlyn

−3.05m

Portsmouth

−2.73m

St. Mary's (local OD)

−2.91m

Southampton

−2.74m

Weymouth

−0.93m

England – East

 

Cromer

−2.75m

Felixstowe

−1.95m

Immingham

−3.90m

Lowestoft

−1.50m

North Shields

−2.60m

Sheerness

−2.90m

Whitby

−3.00m

 

 

Channel Islands

 

St. Helier (local OD)

−5.88m

England – West

 

Blackpool

−4.90m

Formby

−4.93m

Heysham

−4.90m

Hilbre Island

−4.93m

Liverpool

−4.93m

Southport

−4.90m

Workington

−4.20m

 

 

Isle of Man

 

Port Erin (local OD)

−2.75m

Scotland

 

Aberdeen

−2.25m

Kinlochbervie

−2.50m

Leith

−2.90m

Lerwick (local OD)

−1.22m

Millport

−1.62m

Moray Firth

−2.22m

Port Ellen

−0.19m

Portpatrick

−1.80m

Stornoway (local OD)

−2.71m

Tobermory

−2.39m

Ullapool

−2.75m

Wick

−1.71m

Wales

 

Barmouth

−2.44m

Fishguard

−2.44m

Holyhead

−3.05m

Llandudno

−3.85m

Milford Haven

−3.71m

Mumbles

−5.00m

Newport

−5.81m

Northern Ireland

 

(OD Belfast
   = OD Dublin +2.71m)

 

Bangor

−2.01m

Belfast

−2.01m

Donaghadee

−2.26m

Londonderry

−1.61m

Portrush

−1.24m

 

 

Éire / Ireland

 

(OD Dublin)

 

Cobh

+0.13m

Dublin

+0.20m

Limerick

−0.46m

Rosslare

+1.02m

Sligo

+0.69m

Sligo (special datum)

−0.81m