Fertilizer Calculator

The standard application rate for granular lawn fertilizer is 20–40 g/m². A rate of 30 g/m² is safe for most grass and garden plant species. The calculator defaults to 30 g/m², but you can enter the rate recommended by your fertilizer manufacturer.

NPK fertilizers contain nitrogen (N), phosphorus (P) and potassium (K) in varying ratios. Dosing depends on the fertilizer type and the growth stage of your plants. In spring, higher nitrogen rates (up to 40 g/m²) are used; in summer, moderate rates (20–30 g/m²); in autumn, potassium-rich fertilizers. Always read the product label — the rates given are matched to the specific composition.

Measure your lawn area in m² (length × width), then multiply by the recommended rate in g/m². Divide by 1000 to get kilograms. The calculator does this automatically and also shows the amount with a 10% buffer for uneven spreading.

The buffered amount (the "with 10% buffer" field) adds 10% to account for uneven spreading, losses during application, or awkward plot shapes. This ensures you do not run out mid-application — any surplus can be used to top up patchy areas.

Yes — over-fertilization is harmful. It causes fertilizer burn (root and leaf damage from excess mineral salts), and in the case of nitrogen-heavy fertilizers it can trigger excessive vegetative growth at the expense of flowering and fruiting. On lawns, over-dosing causes yellowing and dieback. Always respect the rates on the label.

Granular fertilizers are spread directly onto the soil — they act more slowly but the effect lasts longer (soil application). Liquid fertilizers are applied through watering or spraying — they are absorbed more quickly but require care (easier to burn plants at high concentrations). Granules are most convenient for lawns; liquids suit container plants and fast top-up applications.

The optimal timing depends on plant type. Lawns are fertilized 3–4 times a season: spring (March–April), early summer (June), summer (August) and autumn (September–October). Vegetables are fertilized before planting and during growth. Avoid fertilizing in strong sunlight or drought — best done in overcast weather or in the evening after watering.

The calculator computes fertilizer quantity based on area and application rate — it does not consider soil composition or chemical analysis results. For precision fertilization it is worth having a soil test done every few years (pH, macronutrient content). The results allow you to choose the fertilizer and rate perfectly matched to your garden.

For irregular shapes (L-shapes, trapezoids, circles), divide the plot into simpler figures, calculate their areas separately and add them together. You can also enter an approximate total area — the calculator handles any value. The 10% buffer in the results compensates for any measurement inaccuracies.

For 100 m² at a standard rate of 30 g/m² you need 3000 g, i.e. 3 kg of fertilizer. With the 10% buffer that is 3.3 kg. If you use a fertilizer with a higher rate (e.g. 40 g/m²), you need 4 kg (or 4.4 kg with the buffer). The calculator will work out the exact amount for any area and rate.