pound per acre
Mass per areaexact by definition
The pound per acre is the standard rate unit of North American agriculture. It is exactly 0.45359237 ÷ 4046.8564224 kg/m², about 1.1209 × 10⁻⁴, since both the pound and the acre are exactly defined.
| 1 | 1.1208512 |
The acre began as the area a yoke of oxen could plough in a day — a furlong long by a chain wide, which is why it is 43,560 square feet and not a round number of anything.
About the pound per acre
Every fertiliser recommendation, seed tag and herbicide label in the United States and most of English Canada is written in pounds per acre, and the unit is not going anywhere. It is worth carrying two conversions in your head.
lb/ac → kg/ha: multiply by 1.121. So 150 lb/ac of nitrogen is 168 kg/ha.
lb/ac → g/m²: multiply by 0.112. So the same 150 lb/ac is about 17 g/m², which is the figure to reach for when you are calibrating a spreader over a tarp rather than a field.
The trap is that the ratio is so close to one. A number quoted in the wrong one of these two units is out by only 12%, which is inside the range of a normal agronomic argument and will not announce itself as an error.
One pound per acre in every mass per area unit
| 1.12085 | kilogram per hectare (kg/ha) | |
| 0.00112085 | tonne per hectare (t/ha) | |
| 0.000112085 | kilogram per square meter (kg/m²) | |
| 0.112085 | gram per square meter (g/m²) | |
| 1 | pound per acre (lb/ac)this unit | |
| 0.0005 | short ton per acre (ton/ac) | |
| 0.0229568 | pound per thousand square feet (lb/1000 ft²) | |
| 0.00330579 | ounce per square yard (oz/yd²) | |
| 0.01 | hundredweight per acre (cwt/ac) |