Compound NPK 21-17-17 on 1 m² — 47.6 g for 10 g/m² of N
To put 10 g/m² of N on 1 m² with Compound NPK 21-17-17, spread 47.6 g — that is 47.62 g per m². At 21% content it is simply the 10 g of nutrient you need divided by that figure.
Fertilizer to spread
Urea is only 46% nitrogen, so putting 10 g of N down means spreading 10 ÷ 0.46 = 21.74 g of urea. Multiply instead and you get 4.6 g, a number that looks plausible enough to pass unnoticed. Whenever the content is below 100%, the fertilizer weight is always larger than the nutrient weight — that is the fastest check that you have the division the right way round.
- N 5 g/m² · 23.81 g/m²23.8 g
- N 10 g/m² · 47.62 g/m²47.6 g
- N 15 g/m² · 71.43 g/m²71.4 g
- N 20 g/m² · 95.24 g/m²95.2 g
Comes along with it
Matching 10 g/m² of N with a 21-17-17 puts the fertilizer at 47.62 g/m², and those 47.62 g carry 8.1 g of P₂O₅ and 8.1 g of K₂O with them. You do not get to choose: once the fertilizer weight is fixed, the other two are dragged along in proportion to their content. That is why one compound bag rarely hits all three targets. The order of work is to match one, then top up or accept the surplus with straight fertilizers.
- P₂O₅ 17% · 8.1 g/m²8.1 gP 3.5 g
- K₂O 17% · 8.1 g/m²8.1 gK 6.7 g
- Fertilizer
- Compound NPK 21-17-17 (21-17-17)
- Area
- 1 m²
- Nutrient matched
- N
- Content
- 21%
- Nutrient needed
- 10 g
- Per m²
- 47.62 g
Nearby cells
Same fertilizer, other areas
Same area, other fertilizers
Worth knowing
- Fertilizer to spread = nutrient needed ÷ (content ÷ 100). It is a division, never a multiplication.
- Nutrient needed = area × target rate, so twice the area means twice the fertilizer.
- A fertilizer with half the content takes twice as much for the same nutrient — inverse proportion.
- With a compound, matching one nutrient drags the other two in at their content ratio.
Common questions
Q. How much Compound NPK 21-17-17 goes on 1 m²?
At 10 g/m² of N, 47.6 g — that is 47.62 g per m². It is the 10 g of nutrient needed divided by the 21% content.
Q. If I double the target, do I double the fertilizer?
Yes. Target and fertilizer weight are directly proportional — 5 g/m² takes 23.8 g and 20 g/m² takes 95.2 g. Area behaves the same way: twice the area, twice the fertilizer.
Q. What else goes in along with it?
Matching N to the target also puts in P₂O₅ 8.1 g, K₂O 8.1 g. That is not a choice — those amounts are dragged in at their content ratio.