How to Work Out if It Is Springs or Neaps from the Tidal Range

Subtract today's low water from high water to get the range, then compare it with the port's mean spring and neap ranges. A 4.4 m range at a port with a 4.7 m spring range and 2.2 m neap range is 88% of the way from neaps to springs: close to springs.

The question

Today's tides at a standard port are HW 5.3 m and LW 0.9 m. The port's MHWS is 5.5 m, MHWN 4.4 m, MLWN 2.2 m and MLWS 0.8 m. Is it springs or neaps?

Working, step by step

1. Today's range = 5.3 m − 0.9 m = 4.4 m.
2. Mean spring range = MHWS − MLWS = 5.5 m − 0.8 m = 4.7 m.
3. Mean neap range = MHWN − MLWN = 4.4 m − 2.2 m = 2.2 m.
4. How far from neaps to springs = (4.4 m − 2.2 m) ÷ (4.7 m − 2.2 m) = 0.88.

The tides in this example are made up for practice. For real passages, use official predictions such as ADMIRALTY EasyTide or a nautical almanac, and the port's own tidal curve.

Try it yourself

Put your own numbers into the free tide calculator, which uses the same Rule of Twelfths and works out under-keel clearance.

Learn the method

• Spring and neap tidesGuide
• How to read a tide tableGuide

More worked tide examples

• Height of tide at a given time
• Time the tide reaches a height
• Depth from charted depth
• Under-keel clearance
• Crossing a drying height
• Bridge clearance
• Anchoring depth and scope
• Tidal stream rate from a diamond
• Secondary port: time of HW
• Secondary port: height of HW

Frequently asked questions