Measure it once. Use it often.

Lawn area: rectangles and triangles

Split a lawn into non-overlapping rectangles and triangles. For each piece, measure in one length unit and exclude beds or paving inside it. Add the usable areas yourself. A triangle needs its perpendicular height, not its sloping edge. This estimates area, not a fertilizer application rate.

Rectangle: length × width − excluded area. Triangle: ½ × base × perpendicular height − excluded area.

Examples: 40 ft × 25 ft − 100 sq ft of beds = 900 sq ft. A triangle with a 12 ft base and 8 ft perpendicular height covers 48 sq ft before exclusions.

Sprinkler runtime from catch cups

Use four or more identical, straight-sided containers on a level surface across one sprinkler area. Enter every reading, including zero. Use the same depth unit throughout.

Formula: target depth ÷ average collected depth × test minutes.

Sample size: four readings demonstrate the arithmetic. For a fuller zone audit, Minnesota Extension uses at least 20 containers. The calculator shows lower-quarter uniformity only for 20 or more readings in a count divisible by four. Include zero readings; use one unit throughout.

Lower-quarter uniformity = average of the lowest quarter of readings ÷ average of all readings × 100. Rate per hour = average depth ÷ test minutes × 60. Minnesota Extension: audit method. A calculation is not certification or a water-depth prescription. Account for water already delivered during the test before choosing the additional target.

Choose the additional water target from your grass, soil, recent rain, restrictions and local advice. This calculator does not set a universal weekly allowance. The output estimates runtime for the additional target you entered; the test already applied water. Enter zero when you intend no additional water; it is a valid result, not a reason to choose a minimum watering amount. Pause if runoff begins and reassess coverage before running longer.

Example: 0.2 inches collected in 15 minutes means a 0.3-inch additional target would take about 22.5 minutes at the same rate.

N–P–K nutrient weight in a bag

Calculate label-basis nutrient weights. Enter bag weight and the three guaranteed-analysis percentages. This does not prescribe how much fertilizer your lawn needs.

Formula: bag weight × each label percentage ÷ 100.

Example: 10 lb of 10–0–5 contains 1 lb N, 0 lb P₂O₅ equivalent and 0.5 lb K₂O equivalent. Phosphate and potash results are not elemental phosphorus and potassium weights.

Read the N–P–K explanation and sources · Start with the soil recommendation

Your inputs stay in this page; nothing is submitted. The same percentage arithmetic works in kilograms. Do not compare fertilizer-label percentages directly with soil-test parts per million.

Scale a product-weight rate to your measured area

Use this after selecting a suitable product and confirming its current instructions. Copy a weight of the whole product per stated area, then enter only the turf you will treat. If your recommendation is for actual nitrogen or another nutrient, convert it to a suitable product-weight rate first; those quantities are different.

Formula: stated whole-product weight × actual turf area ÷ area in the stated rate.

Original arithmetic example: a hypothetical rate of 4 lb of product per 1,000 sq ft, used for 350 sq ft, scales to 4 × 350 ÷ 1,000 = 1.4 lb of product. This example does not recommend a material, dose or season. A 10% nitrogen product would contain 0.14 lb of nitrogen in that 1.4 lb; use the separate nutrient-weight calculator to check the analysis.

Keep both area entries in the selected square unit. Enter product weight, rather than a spreader’s numbered setting, a liquid volume, or the headline bag coverage. The result is the total for the area entered. It is not an extra allowance for each pass. Calibration, overlap and label restrictions still matter; this calculation does not establish how evenly a spreader applies material.

Measure rectangles and triangles · Convert a nitrogen recommendation carefully · Use the spreader setup checklist

Penn State Extension: calibration and rate scaling explains why the product, spreader and operator need their own calibration check. Your entries stay in this page; nothing is submitted.

Pure live seed from one label component

Estimate the pure live seed (PLS) represented by one labeled seed component. Use its pure-seed percentage as a proportion of the full bag weight and its own total-germination percentage used for PLS. The result is a label-based weight calculation, not the number of plants that will survive in your lawn.

Check the germination basis: for a tag without a separate hard- or dormant-seed allowance, use the listed germination. USDA NRCS describes total germination for PLS as germination plus separately reported hard and dormant seed. If the label already includes those figures in a total, do not add them again. Ask the supplier or seed lab when the basis is unclear; enter a confirmed total from zero to 100.

Formula: bag weight × pure-seed percentage ÷ 100 × total-germination percentage ÷ 100.

Example: a 10 lb bag with one component at 90% pure seed and 80% germination, with no separate hard or dormant allowance, represents 7.2 lb PLS for that component: 10 × 0.90 × 0.80. The same percentages in a 10 kg bag represent 7.2 kg.

Mixtures: different components can have different germination figures. Do not enter one component’s germination as though it describes the whole mixture. If the label’s purity figure excludes coating or additives, ask the supplier which figure represents the full packaged weight before using this calculation.

Higher PLS does not prove a species fits your shade, climate or use. Keep the species, cultivar, lot number and germination-test date with your repair record. This tool does not adjust a product’s coverage instructions, prescribe a seeding rate or evaluate coating performance.

Method: Penn State Extension: lawn establishment and seed quality; USDA NRCS: total-germination method (September 2006 PDF). The NRCS reference supplies the label method, not a lawn seeding rate. Use the seed-label check when planning a repair.

Your inputs stay in this page; nothing is submitted.