# Altitude Calculator

Manually calculate these questions below to learn , then click to reveal the answer and cross check your answer. Use the above calculator to write enough of your own questions to make sure you learn this.

**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.

## Density Altitude Worked Examples

**Example 1 has pressure and temp both higher than ISA.**

Given QNH 1027 Elev/Alt 1800 OAT 20 Find Pressure and Density Altitude

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 (because 500ft will find temp to nearest 1°C).

e.g. at 1380 ft , nearest 500 ft is 1500 feet, sol lets use 1.5 in the next part.

3. Find ISA temp = 15 - 2 x the thousands of feet (at the PH rounded to 1.5 as per above.)

e.g. 20 C at 1380 = 15 - 2 * 1.5 = 12 (This is what the standard temp should be)

4. Take ISA temp away from current OAT to get deviation from ISA

e.g. 20°C to get ISA deviation = 20° - 12° = 8° ISA dev

5. Multiply ISA deviation by 120 to get pressure correction height 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

Note:

This last answer allows for both the pressure and temperature difference from ISA.

**Example 2 has pressure and temp both lower than ISA.**

Given QNH 1009 Elev/Alt 1800 OAT 6 Find Pressure and Density Altitude

Pressure Height = 1380 ft

Density Height = 2340 ft

1. Find pressure height = Elevation + (1013-QNH) x 30

e.g. 1800 ft at QNH 1009, = 1800+ (1013-1009) x 30 = 1800+ 120 = 1920 ft

2. For the next part of the calculation ONLY, round pressure height to nearest 500ft (because 500ft will find temp to nearest 1°C).

e.g. at 1380 ft , nearest 500 ft is 1500 feet, sol lets use 1.5 in the next part.

3. Find ISA temp = 15 - 2 x the thousands of feet (at the PH rounded to 1.5 as per above.)

e.g. 20 C at 1380 = 15 - 2 * 2 = 11 (This is what the standard temp should be)

4. Take ISA temp away from current OAT to get deviation from ISA

e.g. 20°C to get ISA deviation = 6° - 11° = -5° ISA dev

5. Multiply ISA deviation by 120 to get temp 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. 1920 ft + -600 ft = 1320 ft

**Notes:**

ISA is the international standard atmosphere at AMSL of 15°C and 1013.2 hPa. For every 1000 ft up in altitude temp decreases by 1.98°C, but lets call it 2°C. (Sidenote: Therefore every 500ft is 1°C). For every 1hPA up or down equates to 30 feet.

Steps 1 to 2 deal with the adjustment due to pressure difference from ISA.

Steps 3 to 5 deal with temp difference from ISA.

Step 6 adds the two together so both the pressure and temperature difference from ISA are accounted for to arrive at "density altitude".