Unit Converter — Tool Guide

Who It's For & When to Use It

Airport planners moving between the unit systems that show up across an ALP, a design report, or a planning study. Use it when you need to convert a runway length from feet to meters for an international audience, check an approach speed in kt against an mph figure, estimate the acreage of an RSA or RPZ for land acquisition, translate an FAA surface slope between ratio, percent grade, and degrees, or convert temperature and altimeter pressure for runway-length and performance work. It is the quick, exact-factor utility you reach for between the heavier geometry tools.

How to Use It

1. Choose the unit category. Pick a tab — Distance, Speed, Area, Slope, Temperature, or Pressure. The tool opens on Distance, and your last-used tab is remembered between visits.
2. Enter a value in either field. Each conversion row is bidirectional — type into the left field or the right field and the other side updates live as you type, so there is no "convert" button to press.
3. Pick the conversion pair. Each category lists the relevant pairs directly: feet–meters, feet–nautical miles, statute–nautical miles, statute miles–meters/km, nautical miles–meters/km for Distance; kt–mph, kt–km/h, mph–km/h for Speed; and so on. Use the row whose two units match your task.
4. Read the converted result. Output is shown to 4 significant figures using exact or international-standard conversion factors. The Slope tab is a single three-way group that cross-converts ratio (X:1), percent grade, and degrees from any one input.
5. Copy or swap. The Copy button puts the converted pair on the clipboard with both unit labels; the swap button flips the two fields so you can run the conversion in the other direction. A clear button empties a row.
6. Open a reference table. Each category carries an expandable reference — common runway lengths, AAC approach speed categories, common surface areas, OCS and 14 CFR Part 77 surface slopes, ISA reference temperatures, and standard pressure values. On the Slope tab, click any surface row to load its ratio, percent, and degrees straight into the inputs.
7. Switch categories as needed. Move between tabs to convert different quantities within the same session; the inputs in each tab are independent, so several conversions can stay on screen at once.

Key Features

• Distance. Feet–meters, feet–nautical miles, statute–nautical miles, statute miles–meters, statute miles–kilometers, and nautical miles–meters/kilometers — the length and distance pairs that come up in runway, separation, and navigation work.
• Speed. Knots (kt)–mph, kt–km/h, and mph–km/h, with an AAC approach-speed-category reference (A through E) keyed to threshold-crossing speed.
• Area. Square feet–acres, square feet–square meters, acres–square meters, and acres–hectares — for RSA, RPZ, and OFA area estimates and land-acquisition figures.
• Slope. A three-way group converting ratio (X:1), percent grade, and degrees, with click-to-load AC 150/5300-13B OCS surfaces and 14 CFR Part 77 imaginary surfaces.
• Temperature. Fahrenheit–Celsius, Celsius–Kelvin, and Fahrenheit–Kelvin, with an ISA reference table for runway-length temperature corrections.
• Pressure. Inches of mercury (inHg)–hectopascals/millibars, with a standard-pressure reference anchored to 29.92 inHg = 1,013.25 hPa.
• Exact factors, 4 significant figures. All conversions use exact or international-standard factors; results display to 4 significant figures, and each category's reference note states the governing factors.

FAA References

Unit conversions are exact mathematical relations, not figures fixed by a single Advisory Circular — but the units themselves are the conventions FAA airport design work runs on, and the converter's reference tables and helper text are drawn from them.

• Length in feet. FAA airport design dimensions are stated in feet. The converter uses the international foot (1 ft = 0.3048 m exactly); note that State Plane coordinate work uses US Survey Feet — a ~2 ppm difference, negligible for planning but worth knowing.
• Speed in knots ("kt"). Approach Category boundaries are threshold-crossing speeds (V_at) in kt per AC 150/5300-13B: A < 91, B 91–120, C 121–140, D 141–165, E ≥ 166 kt.
• Area in acres. RPZ acreages in the reference table are per AC 150/5300-13B Appendix G; conversions are exact (1 acre = 43,560 sq ft, 1 ha = 10,000 sq m).
• Slope. OCS slopes (Visual 20:1, NPI/APV 34:1, Precision 50:1, Instrument Departure 40:1) per AC 150/5300-13B Change 1; Part 77 imaginary-surface slopes per 14 CFR Part 77, Subpart C.
• Pressure and temperature. Standard sea-level pressure (29.92 inHg = 1,013.25 hPa) and ISA (15 °C at sea level) per the ICAO Standard Atmosphere — the basis for runway-length temperature and pressure corrections.

Limitations & Disclaimers

AvPlot is technical planning production support — accurate enough for design reports, planning studies, and ALP narratives. It is not a replacement for stamped engineering or construction documents. As the tool itself states: results are for planning and reference, and you are responsible for verifying accuracy before use in any design, construction, or regulatory submittal.

• Conversions are exact mathematical conversions using exact or international-standard factors — they are not subject to interpretation, but they are only as right as the value you enter.
• Results display to 4 significant figures; for official use, verify that the rounding and significant figures match your project's precision requirements rather than carrying the displayed value verbatim.
• The converter does not perform datum or coordinate transformations — length conversions assume the international foot, while State Plane work uses US Survey Feet; use the State Plane and ARP tools for coordinate work.
• Reference-table values (runway lengths, surface areas, surface slopes, standard atmosphere figures) are convenience references; the governing FAA standard always wins over a table cell.

Related Tools

• State Plane Zone Lookup — identify the SPCS83 zone for coordinate work where the foot definition matters (guide).
• ARP Centroid Calculator — compute a proposed Airport Reference Point from runway coordinates (guide).
• RSA / ROFA / ROFZ Reference — the safety-area and object-free-area dimensions whose areas you may convert here (guide).

Tips & Best Practices

• For State Plane and coordinate work, remember the foot definition: this converter uses the international foot, while SPCS83 uses US Survey Feet — the ~2 ppm gap is negligible for planning but can matter at survey precision.
• Use the Slope tab's click-to-load surface rows instead of recalling slope figures — pick the OCS or Part 77 surface and read its ratio, percent, and degrees together, already cross-converted.
• Keep speeds in kt throughout your work to match AAC categories and FAA convention; convert to mph or km/h only for external audiences.
• When sizing land acquisition, convert square feet to acres in the Area tab and sanity-check against the common-surface reference so an RSA or RPZ figure lands in the right order of magnitude.
• Carry the full converted value, then round once at the end — rounding mid-conversion across several steps compounds error; let the 4-significant-figure output be your working precision and round to report precision last.