Area Converter

What this calculates

Enter an area in square millimetres, square centimetres, square metres, hectares, square kilometres, square inches, square feet, square yards, acres or square miles, and this shows it in all ten at once, with each conversion worked through. It also places the area on a scale running from a tenth of a square millimetre to a thousand square kilometres, so a square inch and a square mile can be read against each other.

Every figure comes from exact definitions — nothing is converted with a rounded shortcut factor.

The formula

Every conversion goes through square metres: into square metres with one unit's size, then out again with another's.

The metric units are powers of ten: a square metre is 10,000 cm² or 1,000,000 mm², a hectare is 10,000 m², and a square kilometre is 1,000,000 m², or 100 ha. The imperial units are exact too, and each one builds on the square foot.

Because every factor is exact, a conversion is exact until it is rounded for display — and the calculator rounds each result once, from the exact figure.

Worked example

Not every conversion comes out round. 1 m² is 1 ÷ 0.09290304 = 10.76391 ft² and 1,550.003 in², each shown to seven significant figures, because a square metre is not a whole number of square feet.

Going from an imperial unit into a metric one is exact: 1 ac is 1 × 4,046.8564224 = 4,046.8564224 m² in the working, and 144 in² comes back as exactly 1 ft².

When to use it, and the mistakes to avoid

Use it when a floor plan, a listing or a set of instructions gives an area in a unit you do not think in, when working out how much flooring, paint or turf an area needs, and when a piece of land is described in acres and you think in hectares, or the other way round.

The mistakes that cost the most:

• Using the length factor for an area. A metre is 3.28084 ft, but a square metre is 10.76391 ft² — the factor is squared, because an area is a length times a length. Multiplying 100 m² by 3.28084 gives 328.084, against the true 1,076.391 ft²: less than a third of the real figure.
• Treating acres and hectares as the same. A hectare is about two and a half acres — 2.471054 ac — so 2 ha is 4.942108 ac, not 2. Going the other way, 5 ac is 2.023428 ha.
• Multiplying sides measured in different units. A room 10 ft by 3 m is not 30 of anything: 30 ft² is 2.787091 m² and 30 m² is 322.9173 ft². Convert one side first — 10 ft is 3.048 m — then multiply: 3.048 × 3 = 9.144 m², or 98.4252 ft².
• Expecting every digit of every result. Results are shown to seven significant figures — 1 m² shows as 10.76391 ft² — while the working keeps the exact square-metre figure. An area far too small for a unit, such as 0.000001 mm² in hectares, square kilometres, acres or square miles, reads as 0, and a note under the result says so rather than leaving a silent zero.
• Entering a negative area. An area cannot be less than zero, so the calculator refuses one with a message instead of converting it.

This converter does not include regional land units; it converts the ten units listed above only.

FAQ