How many acres is a hectare? The exact figure, explained

Unlike miles and kilometers, where the exact factor at least terminates cleanly, acres and hectares give you a repeating decimal in both directions: 1 hectare ≈ 2.47105 acres, and 1 acre ≈ 0.404686 hectares. Neither number is a coincidence-free round figure, because the acre and the hectare were never designed to relate to each other — one is a legacy English land unit, the other a purpose-built metric one.

Where the numbers come from

The hectare is simple: exactly 10,000 m², a square 100 meters on a side. The acre is defined instead in square feet: 43,560 ft², or equivalently 1 chain × 1 furlong (66 ft × 660 ft) — a shape and size rooted in pre-industrial ploughing practice. Converted to SI using the exact foot definition (1 ft = 0.3048 m), 1 acre works out to exactly 4,046.8564224 m², a figure documented in NIST Handbook 44. Dividing 10,000 by 4,046.8564224 gives the non-terminating 2.4710538... acres per hectare.

Reference table: acres to hectares

The 640-acre row is a useful landmark: it's exactly one square mile in the US Public Land Survey System, and it converts to just under 259 hectares — a number worth memorizing if you deal with US survey sections and metric land records side by side.

Fast mental-math shortcuts

• Hectares to acres: multiply by roughly 2.5, then subtract about 1%. 10 ha × 2.5 = 25, minus 1% ≈ 24.75, close to the exact 24.71.
• Acres to hectares: multiply by 0.4. 10 acres × 0.4 = 4.0, close to the exact 4.047.

Both shortcuts are fine for a quick sense of scale — walking a property listing, say — but not for a survey, deed, or subdivision plan, where you should use the exact factor via an acre-to-hectare converter rather than a rounded estimate.

A quick sense of scale

One hectare is roughly the size of two American football fields laid side by side (an NFL field including end zones is about 0.53 ha), while one acre is close to three-quarters of a single football field. If you're picturing farmland, a 100-acre parcel is about 40.5 hectares — small by large-scale US or Australian agriculture standards, but a substantial holding almost anywhere else.

Where you'll actually run into this conversion

Beyond farmland, this pair shows up in national park size comparisons, wildfire acreage reports (US sources use acres, many international ones use hectares), and forestry management data. It's also common on real-estate listings for rural property, where the same parcel might be advertised differently depending on the country the buyer platform targets. Whenever you're combining figures from a US source and an international one, converting both to the same unit first — rather than trying to compare “acres” to “hectares” by feel — avoids under- or over-estimating by roughly 2.5x.