# Altitude Calculator

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**This WILL BE IN YOUR PPL EXAM!!!!!** In fact you will likely have 3-4 questions on this.

RPL you will definitely need to know Pressure height!!!!

See worked examples in these expander boxes and some fully worked examples at the bottom of the page.

Pressure Height = 1380 ft

Density Height = 2340 ft

1. Find pressure height = Elevation + (1013-QNH) x 30 e.g. 1800 ft at QNH 1027, = 1800+ (1013-1027) x 30 = 1800+ -420 = 1380 ft

2. For the next part of the calculation ONLY, round pressure height to nearest 500ft

3. Find ISA temp = temp - 2 x the thousands of feet (at the PH) e.g. 20 C at 1380 = 15 - 2 * 1.5 = 12

4. Take ISA temp away from OAT e.g. 20°C to get ISA deviation = 20° - 12° = 8° ISA dev

5. Multiply ISA deviation by 120 to get temperature correction adjustment e.g. 120 x 8 = 960 ft

6. Add pressure correction height to the temp correction adjustment to get density altitude e.g. 1380 ft + 960 ft = 2340 ft

Pressure Height = 3290 ft

Density Height = 3530 ft

1. Find pressure height = Elevation + (1013-QNH) x 30 e.g. 3500 ft at QNH 1020, = 3500 + (1013-1020) x 30 = 3500+ -210 = 3290 ft

2. For the next part of the calculation ONLY, round pressure height to nearest 500ft

3. Find ISA temp = temp - 2 x the thousands of feet (at the PH) e.g. 10 C at 3290= 15 - 2 * 3.5 = 8

4. Take ISA temp away from OAT e.g. 10°C to get ISA deviation = 10° - 8° = 2° ISA dev

5. Multiply ISA deviation by 120 to get temperature correction adjustment e.g. 120 x 2 = 240 ft

6. Add pressure correction height to the temp correction adjustment to get density altitude e.g. 3290 ft + 240 ft = 3530 ft

Pressure Height = 2460 ft

Density Height = 5220 ft

1. Find pressure height = Elevation + (1013-QNH) x 30 e.g. 2400 ft at QNH 1011, = 2400 + (1013-1011) x 30 = 2400 + 60 = 2460 ft

2. For the next part of the calculation ONLY, round pressure height to nearest 500ft

3. Find ISA temp = temp - 2 x the thousands of feet (at the PH) e.g. 33 C at 2460 = 15 - 2 * 2.5 = 10

4. Take ISA temp away from OAT e.g. 33°C to get ISA deviation = 33° - 10° = 23° ISA dev

5. Multiply ISA deviation by 120 to get temperature correction adjustment e.g. 120 x 23 = 2760 ft

6. Add pressure correction height to the temp correction adjustment to get density altitude e.g. 2460 ft + 2760 ft = 5220 ft

Pressure Height = 890 ft

Density Height = 1250 ft

1. Find pressure height = Elevation + (1013-QNH) x 30 e.g. 500 ft at QNH 1000 , = 500 + (1013-1000 ) x 30 = 500 + 390 = 890 ft

2. For the next part of the calculation ONLY, round pressure height to nearest 500ft

3. Find ISA temp = temp - 2 x the thousands of feet (at the PH) e.g. 16 C at 1280 = 15 - 2 * 1 = 13

4. Take ISA temp away from OAT e.g. 16°C to get ISA deviation = 16° - 13° = 3° ISA dev

5. Multiply ISA deviation by 120 to get temperature correction adjustment e.g. 120 x 3 = 360 ft

6. Add pressure correction height to the temp correction adjustment to get density altitude e.g. 890 ft + 360 ft = 1250 ft

Pressure Height = 25000 ft

Density Height = 25600 ft

Note at 1013 hpa Elevation/Altitude = Pressure Height

1. Find pressure height = Elevation + (1013-QNH) x 30 e.g. 25000 ft at QNH 1013 , = 25000 + (1013-1013 ) x 30 = 25000 + 0 = 25000 ft

2. For the next part of the calculation ONLY, round pressure height to nearest 500ft

3. Find ISA temp = temp - 2 x the thousands of feet (at the PH) e.g. -30 C at 25000= 15 - 2 * 25 = -35

4. Take ISA temp away from OAT e.g. -30°C to get ISA deviation = -30° - -35° = 5° ISA dev

5. Multiply ISA deviation by 120 to get temperature correction adjustment e.g. 120 x -5 = 600 ft

6. Add pressure correction height to the temp correction adjustment to get density altitude e.g. 25000 ft + 600 ft = 25600ft