BYTETOOLS

Lawn Fertilizer Calculator

Work out how much fertiliser your lawn needs from the N-P-K analysis and a target nitrogen rate, with bag counts, spreader calibration and an annual programme total.

4.17
Product per 1,000 sq ft (lb)
20.83
Product for the lawn (lb)
1
Bags at 40 lb
$14.58
Cost per application

What actually goes down

Nutrient% in bagApplied to lawn (lb)Per 1,000 sq ft (lb)
Nitrogen (N)24%5.001.00
Phosphate (P₂O₅)4%0.830.17
Potash (K₂O)12%2.500.50

Phosphate and potash come along for the ride — you pick the bag for its nitrogen, and these are what the same amount of product delivers. Many jurisdictions restrict phosphorus on established lawns unless a soil test shows a deficiency, so check before choosing a bag with a middle number above zero.

Bags, spreader setting and the annual programme

83.3
Annual product (lb)
20.00
Annual nitrogen (lb)
$58.33
Annual cost
$2.92
Cost per 1,000 sq ft per feed
1,584
Ground covered per minute (sq ft)
6.60
Product to drop per minute (lb)

Use the per-minute figure to calibrate: weigh a known amount into the hopper, walk for one minute at your normal pace with the gate at the setting on the bag, then weigh what is left. If more or less than this figure went out, adjust the gate and repeat. Spreader numbers on a bag are for that manufacturer's own spreader and rarely transfer.

Product per 1,000 sq ft = target nitrogen × 100 ÷ the N number on the bag, then multiplied by how many 1,000 sq ft units your lawn covers. A 24-4-12 bag at 1 lb of N per 1,000 sq ft therefore needs 4.17 lb of product per 1,000 sq ft. Everything here is a planning estimate: rates depend on grass species, season, soil test results and local nutrient rules, and a soil test is the only way to know whether the P and K are needed at all.

What is the Lawn Fertilizer Calculator?

The ByteTools Lawn Fertilizer Calculator starts where every extension guide starts: a target pound of nitrogen per 1,000 square feet.

  • Product rate from target nitrogen and the N number on the bag, in US or metric units
  • Phosphate and potash actually delivered, shown per lawn and per 1,000 sq ft
  • Bag counts, cost per application and a full annual programme total
  • Spreader calibration: ground covered and product dropped per minute
  • Warns on heavy single feeds and on excessive annual nitrogen
  • Copyable programme summary; everything computed in your browser

How to use the Lawn Fertilizer Calculator

  1. 1

    Pick US or metric units, your currency, and enter the turf area — subtract beds, paths and the driveway.

  2. 2

    Set the target nitrogen per 1,000 sq ft (or per 100 m²) and type in the three N-P-K numbers from the bag.

  3. 3

    Read the product needed per 1,000 sq ft, the total for the lawn, the bag count and the cost per application.

  4. 4

    Check the nutrient table to see how much phosphate and potash the same amount of product delivers.

  5. 5

    Enter bag weight and price, applications per year, spreader swath width and walking speed to get the annual total and the per-minute calibration figure.

About the Lawn Fertilizer Calculator

The ByteTools Lawn Fertilizer Calculator starts where every extension guide starts: a target pound of nitrogen per 1,000 square feet. Divide that by the first number on the bag and you get the product to spread — a 24-4-12 fertiliser at 1 lb of N needs 4.17 lb of product per 1,000 square feet. Enter your lawn area and it scales the whole thing up.

It also shows what else goes down. Phosphate and potash come along for the ride whether you wanted them or not, so the nutrient table reports exactly how much of each lands on the lawn — useful where local rules restrict phosphorus without a soil test. Bag counts, cost per application and an annual programme total round it out.

A spreader panel converts your swath width and walking speed into the product that should leave the hopper each minute, which is how you calibrate rather than trusting the setting printed on a bag. Everything runs locally in your browser with nothing uploaded.

Frequently asked questions

How much fertilizer do I need for 5,000 square feet of lawn?

Multiply the product rate per 1,000 square feet by five. At 1 lb of nitrogen per 1,000 sq ft with a 24-4-12 bag you need 4.17 lb per 1,000, so about 20.8 lb of product for a 5,000 square foot lawn — a little over half a 40 lb bag.

What does the N-P-K number on fertilizer mean?

They are the percentages by weight of nitrogen, available phosphate and soluble potash in the bag. A 24-4-12 bag is 24% nitrogen, so a 40 lb bag contains 9.6 lb of actual nitrogen. Those percentages are exactly what this calculator divides by.

How much nitrogen should I put on my lawn per year?

Most cool-season turf wants 2 to 4 lb of nitrogen per 1,000 square feet a year, split across three to five feeds. More than that buys thatch, disease pressure and leaching rather than colour, which is why the calculator flags heavy programmes.

How do I calibrate my fertilizer spreader?

Weigh a known amount into the hopper, walk one minute at your normal pace with the gate at the bag's setting, then weigh what is left. Compare it against the per-minute figure here and adjust the gate. Spreader numbers on a bag are for that maker's own spreader and rarely transfer.

Can I apply too much fertilizer at once?

Yes. Quick-release products burn turf above roughly 1 lb of nitrogen per 1,000 square feet in a single pass. Split a heavy feed into two lighter applications a few weeks apart, or use a slow-release nitrogen source and water it in.

Do I need the phosphorus in my fertilizer?

Usually not on an established lawn, and many jurisdictions restrict it unless a soil test shows a deficiency. Established turf recycles phosphorus efficiently, so a bag with a middle number of zero is often the right choice. Get a soil test before assuming otherwise.

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