Question 1

How much fertilizer do I need per hectare?

Accepted Answer

It depends on the crop, soil index and fertilizer type. Typical grassland N applications range from 80–200 kg N/ha per year split across 2–3 dressings. Cereals commonly receive 150–220 kg N/ha total. Enter your target application rate (kg/ha or kg/acre) and field size above to calculate the exact tonnage required.

Question 2

How many 25 kg bags of fertilizer do I need?

Accepted Answer

Divide your total kg required by 25. For example, applying 200 kg/ha to a 10 ha field = 2,000 kg total = 80 × 25 kg bags. The calculator shows your total in both kg and tonnes — divide the kg figure by 25 for 25 kg bags, or by 500 for 500 kg bags.

Question 3

What is the nitrogen content of 34.5% ammonium nitrate?

Accepted Answer

34.5% AN contains 345 kg of nitrogen per tonne of product. At a 250 kg/ha application rate you are applying 86.25 kg N/ha. Enter 345 in the N kg/t field above to see the full nutrient breakdown for your field.

Question 4

What is the difference between kg/ha and kg/acre?

Accepted Answer

1 hectare = 2.471 acres, so to convert kg/ha to kg/acre divide by 2.471. For example, 250 kg/ha ÷ 2.471 = 101 kg/acre. The calculator handles this automatically — select your preferred unit in the Rate Unit dropdown and it converts for you.

Question 5

What does NPK mean on a fertilizer bag?

Accepted Answer

NPK stands for Nitrogen (N), Phosphorus (P, expressed as P₂O₅) and Potassium (K, expressed as K₂O). The three numbers on a bag — e.g. 20:10:10 — show the percentage of each nutrient by weight. A 500 kg bag of 20:10:10 contains 100 kg N, 50 kg P₂O₅ and 50 kg K₂O.

Question 6

How do I calculate fertilizer cost per hectare?

Accepted Answer

Multiply your application rate (kg/ha) by the cost per kg. Cost per kg = price per tonne ÷ 1,000. Example: 250 kg/ha at £280/t = (£280 ÷ 1,000) × 250 = £70/ha. Enter cost per tonne in the Cost Breakdown section above and the calculator does this automatically, including cost per acre.

Question 7

How do I calculate how much nitrogen I am applying per hectare?

Accepted Answer

Multiply the application rate (kg/ha) by the N content of the product (kg N per tonne) then divide by 1,000. Example: 250 kg/ha of 34.5% AN (345 kg N/t) = 250 × 345 ÷ 1,000 = 86.25 kg N/ha. Enter the N kg/t value in the Nutrient Composition section above and the calculator shows this automatically.

Question 8

What is the nitrogen limit for UK farms in NVZ areas?

Accepted Answer

Under the UK Nitrates Regulations, farms in Nitrate Vulnerable Zones are limited to an average of 170 kg total nitrogen per hectare per year from all organic manure sources. Manufactured fertilizer N is additional to this, but total crop N recommendations from AHDB RB209 should still be followed to avoid over-application. Use our NVZ Compliance Check tool to calculate your whole-farm N loading.

Artificial Fertilizer Calculator

Application Rate & Field Size

Nutrient Composition

Cost Breakdown

Common UK Fertilizer NPK Values

Fertilizer Calculator — Frequently Asked Questions

Fertilizer	N kg/t	P kg/t	K kg/t	S kg/t	Notes
34.5% AN	345	—	—	—	Most common UK straight N
Urea 46N	460	—	—	—	Higher N%, volatilisation risk
CAN 26N	260	—	—	—	Calcium ammonium nitrate
NPK 20:10:10	200	100	100	—	Balanced compound
NPK 27:5:5	270	50	50	—	High-N compound for grass
DAP 18:46:0	180	460	—	—	High phosphate, starter fert
Triple Super	—	460	—	—	0:46:0 straight phosphate
MOP 0:0:60	—	—	600	—	Muriate of potash
SOP 0:0:50	—	—	500	48	Sulphate of potash + S