What is 50 units of nitrogen per acre in kg/ha?

50 units of nitrogen per acre equals 56.1 kg N/ha. One unit of nitrogen is one pound of nutrient per acre. To convert units per acre to kg/ha, multiply by 1.121. So 50 × 1.121 = 56.1 kg/ha. The same conversion applies to phosphate (P₂O₅) and potash (K₂O).

What is a hundredweight (cwt) in kg?

One UK imperial hundredweight (cwt) is 112 pounds, equal to 50.8 kg. Despite the name suggesting 100 pounds, the imperial hundredweight is 112 lb — defined as eight stone of 14 pounds each. The US hundredweight is 100 pounds, so always check which is used in older manuals or imported equipment documentation.

How do I convert bushels per acre to tonnes per hectare for wheat?

For wheat, multiply bushels per acre by 0.0672 to get tonnes per hectare. This is based on the standard UK wheat bushel weight of 60 lb (27.2 kg). A yield of 40 bushels per acre — historically considered a good crop — equals approximately 2.7 t/ha. Barley and oats have different bushel weights, so the conversion factor differs by crop.

How do I convert gallons per acre to litres per hectare?

Multiply gallons per acre by 11.23 to get litres per hectare. This is based on the UK imperial gallon of 4.546 litres and the 2.471 acres-per-hectare factor. A water volume of 20 gallons per acre — a common old boom sprayer output — equals approximately 224 litres per hectare.

What does a "unit" of nitrogen mean in old UK farm records?

In old UK farming, a unit of any nutrient means one pound of that nutrient element per acre. It applies equally to nitrogen (N), phosphate (P₂O₅) and potash (K₂O). The unit system was standard before metrication and is still used informally by many older farmers. Multiply units per acre by 1.121 to convert to kg/ha.

How do I convert hundredweights per acre to kg/ha?

Multiply hundredweights per acre by 125.5 to get kg/ha. This combines the cwt-to-kg factor (50.8) with the acres-to-hectare factor (2.471). So three hundredweights of lime per acre — a common old liming recommendation — equals approximately 376 kg/ha.

What is muriate of potash?

Muriate of potash is the old name for potassium chloride (KCl) — now sold as MOP (Muriate of Potash) — containing approximately 60% K₂O. The name comes from muriatic acid (hydrochloric acid) historically used in its production. It is still widely sold today under the MOP abbreviation.

What is the difference between an imperial ton and a metric tonne?

An imperial ton is 2,240 pounds (20 hundredweights), equal to 1,016 kg. A metric tonne is exactly 1,000 kg. The difference is approximately 1.6%, so for most farm planning purposes old tonnage figures can be treated as roughly equivalent to metric tonnes. For precise calculations, multiply imperial tons by 1.016.

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50 Units of N Per Acre — Old UK Farming Measurements Explained & Converted to Metric

If you've opened an old spray record book and found applications in gallons per acre, or read a soil report recommending three hundredweights of lime per acre, this guide converts every common old UK farming measurement to modern metric — with quick-reference tables for the farm office or cab.

Quick Reference — Common Conversion Multipliers

To Convert	Multiply By
Units per acre → kg/ha	× 1.121
cwt per acre → kg/ha	× 125.5
Gallons per acre → litres/ha	× 11.23
Pints per acre → litres/ha	× 1.404
Bushels/acre (wheat) → t/ha	× 0.0672
Acres → hectares	× 0.4047
Hectares → acres	× 2.471
Gallons → litres	× 4.546
Pounds (lb) → kg	× 0.4536
cwt → kg	× 50.80
Imperial tons → tonnes	× 1.016

What Is a Unit of Nitrogen — and What Is 50 Units Per Acre in Metric?

This is the most common conversion question in UK farming, and the one that catches most people out.

One unit of nitrogen is one pound of nutrient per acre.

A "unit" simply means one pound of the nutrient element — nitrogen, phosphorus or potassium — applied per acre. It's not a bag size or a product rate. The same definition applies to phosphate (P₂O₅) and potash (K₂O).

To convert units per acre to kg/ha, multiply by 1.121.

Units Per Acre	kg/ha
10 units/acre	11.2 kg/ha
20 units/acre	22.4 kg/ha
30 units/acre	33.6 kg/ha
40 units/acre	44.8 kg/ha
50 units/acre ← the common question	56.1 kg/ha
60 units/acre	67.3 kg/ha
80 units/acre	89.7 kg/ha
100 units/acre	112.1 kg/ha
120 units/acre	134.5 kg/ha
150 units/acre	168.2 kg/ha
200 units/acre	224.2 kg/ha

So when an old recommendation says "50 units of N per acre for first cut silage," it means 56 kg N/ha in modern terms.

What Is a Hundredweight (cwt)?

A hundredweight — abbreviated cwt — is 112 pounds, or 50.8 kg. Despite the name suggesting 100 pounds, the imperial hundredweight is 112 lb, historically defined as eight stone of 14 pounds each. The US hundredweight is 100 pounds — a source of confusion when reading older American machinery manuals.

In UK farming the hundredweight was the standard unit for fertiliser bag sizes, lime applications, grain yields, root crop yields and concentrate feed — before 50 kg bags became standard through the 1970s and 80s.

Hundredweight Conversions

Imperial	Metric
1 cwt (hundredweight)	50.8 kg
1 quarter	12.7 kg (¼ cwt)
1 stone	6.35 kg
1 ton (imperial)	20 cwt = 1,016 kg
1 lb (pound)	0.454 kg

Hundredweights Per Acre to kg/ha

To convert cwt/acre to kg/ha, multiply by 125.5.

cwt Per Acre	kg/ha
1 cwt/acre	125.5 kg/ha
2 cwt/acre	251 kg/ha
3 cwt/acre	376 kg/ha
4 cwt/acre	502 kg/ha
5 cwt/acre	628 kg/ha

"Three hundredweights of lime per acre" is approximately 376 kg/ha — useful when cross-referencing old liming records against current soil pH data.

Old Fertiliser Bag Rates — Decoded

Before 50 kg bags became standard, fertiliser was sold in hundredweight bags at rates expressed in bags or cwt per acre.

Old Recommendation	What It Means	Modern Equivalent
2 cwt of 20:10:10 per acre	2 × 50.8 kg = 101.6 kg/acre of NPK 20:10:10	251 kg/ha of 20:10:10
3 cwt of Nitram per acre	151 kg/acre of ammonium nitrate (34.5% N)	374 kg/ha = 129 kg N/ha
1 cwt of muriate of potash per acre	50.8 kg/acre of MOP (60% K₂O)	126 kg/ha MOP = 75 kg K₂O/ha
2 bags of superphosphate per acre	Typically 2 cwt = 101 kg/acre (18% P₂O₅)	251 kg/ha = 45 kg P₂O₅/ha

"Muriate of potash"

The old name for potassium chloride (KCl) — now sold as MOP. Contains approximately 60% K₂O. Still available under the MOP name today. The name comes from muriatic acid used in its production.

"Nitram"

Still in use today as a brand name for ammonium nitrate (34.5% N). The rate expression has changed from cwt/acre to kg/ha — but the product itself is unchanged.

Grain Yields — Bushels Per Acre to Tonnes Per Hectare

Old yield records and historical farm books express grain yields in bushels per acre. A bushel is a volume measure but was used as a weight measure with a different standard weight for each crop.

Bushel Weights by Crop

Crop	kg / bushel	lb / bushel
Wheat	27.2 kg	60 lb
Barley	21.8 kg	48 lb
Oats	14.5 kg	32 lb
Rye	25.4 kg	56 lb
Oilseed rape	22.7 kg	50 lb
Peas	27.2 kg	60 lb
Maize	25.4 kg	56 lb

Wheat — Bushels Per Acre to t/ha

Bushels/Acre (wheat)	t/ha	Note
20 bu/acre	1.34 t/ha
30 bu/acre	2.01 t/ha
40 bu/acre	2.68 t/ha	Old "good yield" benchmark
50 bu/acre	3.35 t/ha
60 bu/acre	4.02 t/ha
80 bu/acre	5.36 t/ha
100 bu/acre	6.7 t/ha

A wheat crop of "40 bushels to the acre" — historically a good yield — is approximately 2.7 t/ha in modern terms. For barley, divide by 1.25. For oats, divide by roughly 1.88.

Old Spray Records — Gallons and Pints Per Acre

Old spray record books are one of the most common places to encounter imperial measurements. Water volumes were recorded in gallons per acre; product rates in pints or fluid ounces per acre.

1 gallon

4.546 litres

1 pint

568 ml

1 fluid ounce

28.4 ml

Gallons Per Acre → Litres Per Hectare

Multiply gallons per acre by 11.23.

Gallons/Acre	Litres/ha	Note
5 gal/acre	56 l/ha
10 gal/acre	112 l/ha
15 gal/acre	168 l/ha
20 gal/acre	224 l/ha	Common old boom sprayer output
30 gal/acre	337 l/ha
40 gal/acre	449 l/ha

Product Rates — Pints and Fluid Ounces Per Acre

Old Rate	Litres/ha	ml/ha
1 fl oz/acre	—	70 ml/ha
4 fl oz/acre	—	280 ml/ha
8 fl oz/acre	—	562 ml/ha
1 pint/acre	1.40 l/ha	1,404 ml/ha
2 pints/acre	2.81 l/ha	—
1 quart/acre	2.81 l/ha	—
1 gallon/acre	11.23 l/ha	—

When cross-referencing old spray records against current product labels, note that many older active ingredients are no longer approved. An old recommendation for "8 fl oz of Gramoxone per acre" is a paraquat application — banned in the UK since 2007.

Area Measurements — Acres, Roods and Perches

The acre remains in daily use on UK farms and needs no conversion for most purposes — but older records and some land deeds use subdivisions that are now rarely seen.

Unit	Modern Equivalent	Notes
1 acre	0.405 ha / 4,047 m²	Still in common use
1 rood	0.101 ha / 1,012 m²	Quarter of an acre
1 perch	25.3 m²	1/160th of an acre
1 chain	20.1 m (length)	Old surveying unit
1 furlong	201 m (length)	One eighth of a mile
1 square chain	404.7 m²	1/10th of an acre

Example: old field record

"12 acres, 2 roods and 16 perches" = 12 + 0.5 + (16 × 1/160) = 12.6 acres (5.1 ha)

Acres to Hectares Quick Reference

Acres	Hectares
1 acres	0.4 ha
5 acres	2.02 ha
10 acres	4.05 ha
20 acres	8.09 ha
50 acres	20.23 ha
100 acres	40.47 ha
200 acres	80.94 ha
500 acres	202.34 ha

Use the Field Size Converter to convert any field area between acres and hectares instantly.

Old Liveweight and Milk Yield Measures

Liveweight

Livestock were traditionally weighed and sold in stones and hundredweights. Old pedigree herd books and liveweight records will reflect this.

Old Measure	Metric
1 stone	6.35 kg
1 score (20 lb)	9.07 kg
1 hundredweight	50.8 kg
20 stone bullock	127 kg
10 cwt fat steer	508 kg

Milk Yield — Gallons to Litres

Older milk records express yield in gallons per cow per day or per lactation.

Imperial	Litres
1 gallon milk	4.546 litres
500 gal / lactation	2,273 litres
1,000 gal / lactation	4,546 litres
1,200 gal / lactation ← old "good cow" benchmark	5,455 litres
1,500 gal / lactation	6,819 litres

A cow recorded as "1,200 gallons" in an old herd book was producing approximately 5,455 litres per lactation — a respectable yield by 1970s–80s standards.

Useful for farm record work

Scientific Pocket Calculator

Useful for doing unit conversions in the farm office or cab.

Farm Record Book

Dedicated field diary for logging spray records, yields and applications.

Digital Measuring Wheel

Measure field perimeters and distances accurately for area calculations.

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Frequently Asked Questions

Conversions are based on standard UK imperial definitions. The imperial hundredweight (112 lb) differs from the US short hundredweight (100 lb). Bushel weights are standard UK trade weights. Always verify historical spray records against current product approvals before use.