Fertiliser Calculator (South Africa)
Work out how many bags of fertiliser you need and what they cost, in elemental South African N-P-K, plus the cost per kilogram of nutrient and a soil-test plan checker.
South African fertiliser is labelled in elemental N, P and K, not the oxide form (P₂O₅, K₂O) used on most international calculators, so a generic tool will quietly overstate your phosphorus and potassium. This one uses real South African grades and prices, works out the bags and cost, and shows you the number that actually lets you compare products: the cost per kilogram of nutrient.
Tap a common South African product above to fill it in one click, or pick any grade, straight or custom mix from the list. Grades like 5:1:5 come in different strengths, so check the bracket number, the total plant food %, printed on your bag.
The bracket number, total plant food %.
N %
P %
K %
1 hectare = 10 000 m².
From your soil test, co-op recommendation, or the product label. Not a rate you should guess.
| Nutrient (elemental) | Per hectare | Total applied |
|---|
This is the number that lets you compare unlike products fairly. Two bags at the same price are not equal value if one is half filler. A cheaper bag with more nutrient in it is the better buy.
| Measure | Cost |
|---|
Enter the nutrient targets from your soil test or co-op recommendation, then add the products you plan to use. This checks whether your plan actually delivers what the soil asked for, it does not invent a recommendation for you. For that you need a proper soil analysis.
Leave this off for a South African soil lab report, which uses elemental P and K. Tick it only if your recommendation came from an international source or an older report quoting P₂O₅ and K₂O.
Estimates to help you budget and buy, not a substitute for a soil test or advice from an agronomist. Fertiliser rates should come from a soil analysis for your land and crop, over-application wastes money and can damage soil and water. Reference prices are bulk commodity figures from SA Grain, July 2026, retail bag prices are higher, so enter your own quote for accuracy. Last reviewed July 2026.
💬 Discuss this tool, or check the numbers against your own fertiliser quote, on the forum →
How to work out your fertiliser, the South African way
Buying fertiliser comes down to two questions, how many bags do I need, and am I getting value for money. The bag count is simple arithmetic, your rate in kilograms per hectare times your hectares, divided by the bag size, rounded up. The value question is where most farmers lose money, because two bags at the same price are not equal if one holds far more actual nutrient than the other. The calculator above answers both, and it does the value comparison the way that actually matters, on cost per kilogram of nutrient rather than cost per bag.
There is a South African wrinkle that trips up anyone using an international calculator. Here fertiliser is labelled in elemental form, plain N, P and K, while most of the world quotes phosphorus and potassium as oxides, P₂O₅ and K₂O, which are larger numbers for the same amount of nutrient. Apply an oxide based recommendation as if it were elemental and you will over-apply, and over-application wastes money and can harm your soil and nearby water. This tool works in elemental N, P and K throughout, with a toggle in the soil test tab to convert an oxide recommendation across correctly.
The grade codes make more sense once you know the pattern. A grade like 4:3:4 (33) is a ratio of four parts nitrogen to three parts phosphorus to four parts potassium, and the bracketed 33 is the total plant food percentage, so the rest of the bag is carrier material. The same reading works for every grade, so a bag marked 2:3:2 (22) or 3:2:1 (25) is a common planting mixture, and a code like 5:1:5 simply means five parts nitrogen and potassium to one part phosphorus, but always check the bracket number on your own bag, because a grade such as 5:1:5 is sold in more than one strength. Straight products are simpler, LAN is 28 percent nitrogen, urea is 46 percent, MAP carries phosphorus with a little nitrogen, and potassium chloride, the common potash, is about 51 percent potassium. The calculator holds the common South African grades and straights, and you can enter a custom grade or your own analysis for anything not listed.
One thing this tool deliberately will not do is tell you how much to apply. The right rate depends on your soil, your crop and your yield goal, which is what a soil test is for. What it will do is take a rate you already have, from that soil test or your co-op, and turn it into bags, rands, and an honest nutrient breakdown, then let you check a multi-product plan against the target. If the codes on the bag are new to you, our guide to fertiliser grades and prices in South Africa explains what numbers like 2:3:2 and 3:2:1 mean, and what the common products cost. If your soil is acidic, our Lime Calculator works out tons, bags and cost per effective tonne using the South African acid saturation method. While you are here you can also work out what your borehole pump costs to run, check whether solar would pay off on your farm, or browse all our free South African tools and calculators.
Reference fertiliser prices in South Africa (July 2026)
These are bulk commodity reference prices from SA Grain, handy as a sanity check when you weigh up a quote. Retail bag prices are higher, so for an accurate cost enter your own price in the calculator above. Fertiliser, also spelled fertilizer, is traded globally, so these numbers move with the dollar, shipping and the local market.
| Product | Per ton | Per 50 kg bag |
|---|---|---|
| LAN (28% N) | R19 125 | R956 |
| Urea (46% N) | R21 009 | R1 050 |
| MAP (11% N, 22% P) | R22 860 | R1 143 |
| Potassium chloride / MOP / potash (51% K) | R11 242 | R562 |
Frequently asked questions
How do I work out how many bags of fertiliser I need?
Multiply your application rate in kilograms per hectare by the number of hectares to get the total kilograms, then divide by your bag size and round up to the next whole bag. As an example, 300 kg per hectare across 5 hectares is 1 500 kg, which is 30 bags of 50 kg. The calculator above does this for you and also works out the cost, but the rate itself should come from a soil test or a co-op recommendation, it is not a number to guess at.
What does a fertiliser grade like 3:2:1 (25) mean?
The three numbers are the ratio of nitrogen to phosphorus to potassium, and the number in brackets is the total plant food as a percentage of the bag. For 3:2:1 (25) the parts add up to six, so nitrogen is three sixths of 25 percent, which is 12.5 percent, phosphorus is two sixths, about 8.3 percent, and potassium is one sixth, about 4.2 percent. So a 50 kg bag of 3:2:1 (25) holds roughly 6.25 kg of nitrogen, 4.2 kg of phosphorus and 2.1 kg of potassium, the rest is carrier material. The calculator shows this breakdown for whichever product you pick.
Why is South African fertiliser labelled differently from international products?
South Africa expresses phosphorus and potassium in elemental form, as P and K, while most of the world, including the United States, uses the oxide form, P₂O₅ and K₂O. That matters because the oxide numbers are bigger for the same amount of actual nutrient. If you take a recommendation or use a calculator built for oxide figures and apply it as if it were elemental, you will over-apply phosphorus and potassium and waste money. To convert, multiply P₂O₅ by 0.436 to get P, and K₂O by 0.830 to get K. The soil test tab above has a toggle that does this for you.
How do I turn a soil test recommendation into actual fertiliser to buy?
A soil test gives you a target in kilograms of nitrogen, phosphorus and potassium per hectare. You then pick products whose nutrients add up to that target. The soil test tab above lets you enter your target and then add the products and rates you are considering, and it shows whether your plan meets, falls short of, or overshoots each nutrient. It deliberately does not invent a recommendation for you, because the right rates depend on your specific soil, crop and yield goal, which only a proper soil analysis can tell you.
Is urea or LAN cheaper for nitrogen?
Compare them on cost per kilogram of nitrogen, not on the price of the bag. Urea is 46 percent nitrogen while LAN is only 28 percent, so even when a bag of urea costs more, each kilogram of nitrogen from urea is usually cheaper. At the July 2026 reference prices that works out to roughly R46 a kilogram of nitrogen from urea versus about R68 from LAN. LAN still has its place, it is gentler on the soil and less prone to volatilising away in hot dry conditions, but purely on the nitrogen price urea normally wins. The calculator shows this cost per kilogram of nutrient for whatever product you select.
How much nitrogen is in a 50 kg bag of LAN or urea?
LAN is 28 percent nitrogen, so a 50 kg bag holds 14 kg of nitrogen. Urea is 46 percent nitrogen, so a 50 kg bag holds 23 kg. That difference is exactly why the two products are priced and applied so differently, and why comparing them on the bag price alone is misleading. Work in kilograms of actual nutrient and the picture changes.
How much fertiliser does maize or another crop need per hectare?
There is no single correct figure, and anyone who gives you one without seeing your land is guessing. The right rate depends on what your soil already holds, your target yield, the rainfall or irrigation you have, and your crop. That is why a soil test is the starting point for any fertiliser plan, and why the Fertiliser Association of Southern Africa and every co-op agronomist push soil sampling first. This calculator turns a rate you already have into bags and cost, it does not set the rate for you. Treat any general rule of thumb as a rough sanity check only, not a recommendation.
Why have fertiliser prices in South Africa been so high?
Fertiliser is a globally traded commodity priced in dollars, so local prices move with international nitrogen, phosphate and potash markets, the rand exchange rate, and shipping costs, none of which are under local control. Prices spiked sharply after 2022 and, while they have eased from the peak, they were still running well above the level of a year earlier through 2026. Because the numbers move around so much, the calculator lets you type in your own current quote rather than relying only on the built in reference figures, which are bulk commodity prices and lower than what you pay for retail bags.
What are fertiliser prices per ton and per 50 kg bag in South Africa?
Fertiliser prices move constantly because it is a globally traded commodity priced in dollars. As a July 2026 reference, LAN (28% N) was about R19 125 a ton and urea (46% N) about R21 009, which is roughly R956 and R1 050 for a 50 kg bag. The reference price table above lists MAP and potassium chloride as well. These are bulk commodity figures, so retail bags cost more, and it is also why local fertilizer prices can swing sharply from one season to the next. Enter your own quote in the calculator for an accurate cost.
This calculator gives estimates to help you budget and buy, it is general information and not a substitute for a soil analysis or advice from a qualified agronomist. Fertiliser rates should come from a soil test for your own land and crop. Nutrient contents are typical South African values and reference prices are bulk commodity figures from SA Grain, July 2026, retail bag prices are higher, so enter your own quote for accuracy. Last reviewed July 2026.