Zerdly

Survey Unit Consistency Checker

Checks that the units in a survey calculation have matching dimensions before combining them, and converts lengths, areas, volumes and angles.

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How to use this calculator

Check a calculation

Each value's dimension is checked before anything is combined.

Enter the values to check.

Consistent units do not prove the values share a coordinate system, or that the observations behind them are any good.

Check a table of quantities

Name each quantity, enter its value and unit, and (optionally) the dimension it must have. Every row is checked before it is normalised; nothing is combined.

The CSV keeps each original value and unit beside the normalised value; text cells that a spreadsheet would run as a formula are prefixed with an apostrophe. Matching units do not prove matching coordinate systems or good observations.

Convert one value

  • millimetre (mm)1500
  • centimetre (cm)150
  • metre (m)1.5
  • kilometre (km)0.0015
  • inch (in)59.05511811
  • foot, international (ft)4.921259843
  • US survey foot (legacy) — legacy4.92125
  • yard (yd)1.640419948
  • chain, Gunter's (66 ft)0.07456454307
  • mile (mi)0.0009320567884
  • nautical mile (nmi)0.0008099352052

The international foot is exactly 0.3048 m. The US survey foot (1200/3937 m) is a legacy unit, about 2 ppm longer — 2 cm in 10 km.

How the method works

A fixed worked example to explain the method — it is not your result.

Check dimensions before combining values
Illustrative method
Check dimensions before combining valuesTwo worked sums: 100 cm plus 1 m converts to a common unit and gives 2 m; 1 m plus 1 square metre is refused because length and area are different dimensions.100 cm + 1 mL + L → convert: 1 m + 1 mdimensions agree= 2 m ✓1 m + 1 m²L + L² → no common unitdimension mismatchinvalid ✕
100 cm + 1 m: both are length (L), so convert to metres first — 1 m + 1 m = 2 m. 1 m + 1 m²: length (L) and area (L²) are different dimensions, so there is no answer to convert to.

Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.

How to use this calculator

  1. Choose an operation — add distances, height difference, area, volume, add angles or scale factor.
  2. Enter each value with its own unit. Every value's dimension is checked before anything is combined.
  3. Read the result in any unit of the right dimension, and open the conversion ladder to see each value in canonical units.
  4. If a value has the wrong dimension, the tool says which row and offers a fix you can apply with one click. Below, the converter shows any single value in every unit of its kind.
  5. For a whole list, use the quantity table: name each quantity, give its value, unit and (optionally) the dimension it must have. Each row is checked, the same quantity in two dimensions is flagged, and the normalised values download as CSV with the original value and unit beside them.

How it works

Every unit carries a dimension — length, area, volume, angle or unitless — and an exact defining constant. Values are converted to metres, square metres, cubic metres or radians before they are combined.

An operation checks its operands first: '1 m + 1 m²' is refused, not computed. Area and volume units have their own constants (1 ft² = 0.3048² m²), so a length factor is never applied once to an area.

The international foot is exactly 0.3048 m. The US survey foot, 1200/3937 m, is labelled legacy: it is about 2 ppm longer, or 2 cm in 10 km.

Consistent units do not prove that values share a coordinate system, or that the observations behind them are sound.

Worked example

100 cm + 1 m, then 1 m² + 1 m. 100 cm + 1 m = 2 m. Changing the first unit to m² stops the calculation: row 1 is an area, but adding distances needs a length — and 'Use m' is offered as the fix. In the converter, 200 gon is 180° and π rad.

Common mistakes

  • Converting an area with the length factor once (1 ft² ≠ 0.3048 m²).
  • Mixing international and US survey feet in one job.
  • Adding a height difference in millimetres to one in metres without converting.

Frequently asked questions

What is a gon?

A gon (or grad) divides a circle into 400 parts, so a right angle is 100 gon and a full circle 400 gon. Some European instruments and software use it instead of degrees.

Is this official course material?

No. It is free study support mapped to surveying course levels — not official North Metropolitan TAFE content or advice. Always follow your lecturer and the official assessment brief, and check your own working.

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Cite this tool

Zerdly. (2026). Survey Unit Consistency Checker. Retrieved from https://www.zerdly.com/tools/survey-unit-consistency-checker/

Tip: Enter any known values to calculate the remaining results.

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