Sailing boat – speed triangle
Navigation tool

Speed triangle  ·  Distance, speed and time

Fill in two of the three fields in the triangle – the third is calculated automatically. An indispensable aid for route planning, arrival time calculation and speed estimation.

D = Distance (nautical miles) F = Speed (knots) T = Time (decimal hours)
Try examples
Aarhus → Tunø
When do we arrive?
D = 22 nm F = 6 kn T = ?
Race against the tide
What speed is needed?
D = 15 nm F = ? T = 2 hours
Evening sail
How far can we get before dark?
D = ? F = 5 kn T = 3,5 hours
Y3 planning exercise
Departure 08:00 – arrival time?
D = 35 nm F = 7 kn T = ?
Interactive triangle
Distance
D
nautical miles
Speed
F
knots
Time
T
decimal hours
✓
Understanding the triangle
D
Distance
D = F × T
Multiply the speed (knots) by the passage time (hours). The result is the distance in nautical miles.
F
Speed
F = D ÷ T
Divide the distance (NM) by the passage time (hours). Gives the required speed in knots.
T
Time
T = D ÷ F
Divide the distance (NM) by the speed (knots). Gives the passage time in decimal hours.

⏱ Time conversion

Decimal hours ↔ hours:minutes

115 min ÷ 60 = 1,92 hours

1,75 hours × 60 = 105 min = 1h 45min

The calculator automatically shows both formats when T is calculated.

Log vs. chart: The log measures distance sailed through the water. The chart works with distance over the ground. Current affects the difference – see the current triangle for corrections.