# Lawn Seed and Fertilizer Calculator

> Computes the grass seed needed for a new lawn or overseeding from the area and the species' seeding rate (Penn State and UF/IFAS extension rates in lb per 1,000 ft²), and the fertilizer needed to apply a target amount of nitrogen from the N percentage on the bag.

- Calculator id: `lawn-seed-fertilizer` · Category: Everyday Life (`everyday`) · Tool name: `estimate_lawn_seed_and_fertilizer`
- Canonical page: https://tttkmbb.com/everyday/lawn-seed-fertilizer · This document: https://tttkmbb.com/everyday/lawn-seed-fertilizer.md · JSON definition: https://tttkmbb.com/everyday/lawn-seed-fertilizer.json

## Purpose

Computes the grass seed needed for a new lawn or overseeding from the area and the species' seeding rate (Penn State and UF/IFAS extension rates in lb per 1,000 ft²), and the fertilizer needed to apply a target amount of nitrogen from the N percentage on the bag.

**Use when:** You are seeding or overseeding a lawn of known size and need to know how many pounds or kilograms of seed and of a given N-P-K fertilizer to buy.

**Do not use when:** You are laying sod or turf rolls, need a soil-test-based lime or phosphorus recommendation, or want spacing for individual plants (use plant-spacing).

## Input

| Parameter | Type | Unit | Required | Description |
| --- | --- | --- | --- | --- |
| `area` | number |  | required | Area to seed, in the chosen unit. (> 0, max 10000000) |
| `area_unit` | enum: ft2 \| m2 |  | optional, default "ft2" | Unit of area. |
| `grass_type` | enum: kentucky_bluegrass \| tall_fescue \| perennial_ryegrass \| fine_fescue \| mix_cool_season \| bermuda \| bahia \| centipede |  | required | Grass species or mixture; sets the seeding rate for a new lawn. |
| `seeding` | enum: new_lawn \| overseed |  | optional, default "new_lawn" | New lawn on bare soil, or overseeding into existing grass at half the rate. |
| `fertilizer_n_percent` | number | % | optional, default 24 | First number of the N-P-K analysis on the bag (24 for a 24-0-4 fertilizer). (> 0, max 100) |
| `target_n_lb_per_1000ft2` | number | lb N/1000 ft² | optional, default 1 | Nitrogen to apply per 1,000 ft² in this application; starter applications use 0.5–1 lb. (> 0, max 3) |

## Output

| Field | Type | Unit | Description |
| --- | --- | --- | --- |
| `area_ft2` | number | ft² | Lawn area in square feet. |
| `area_m2` | number | m² | Lawn area in square metres. |
| `seed_rate_lb_per_1000ft2` | number | lb/1000 ft² | Rate applied (half the new-lawn rate for overseeding). |
| `seed_rate_g_per_m2` | number | g/m² | Same rate in grams per square metre. |
| `seed_lb` | number | lb | seed_rate × area_ft2 / 1000. |
| `seed_kg` | number | kg | Seed in kilograms. |
| `fertilizer_rate_lb_per_1000ft2` | number | lb/1000 ft² | target_n × 100 / fertilizer_n_percent. |
| `fertilizer_rate_g_per_m2` | number | g/m² | Same rate in grams per square metre. |
| `fertilizer_lb` | number | lb | fertilizer_rate × area_ft2 / 1000. |
| `fertilizer_kg` | number | kg | Fertilizer in kilograms. |
| `nitrogen_lb` | number | lb | target_n × area_ft2 / 1000. |
| `bags_note` | string |  | Quantities to buy and the application limit. |

## Formula

`area_ft2 = area (× 10.7639 if m²); seed_lb = rate_lb_per_1000ft2 × (0.5 if overseed) × area_ft2 / 1000; fertilizer_lb = target_n_lb_per_1000ft2 × 100 / fertilizer_n_percent × area_ft2 / 1000; kg = lb × 0.45359237; g/m² = lb/1000 ft² × 4.882`

New-lawn rates are the midpoints of the extension ranges (Penn State for cool-season species, UF/IFAS for warm-season species); overseeding uses half the rate as a rule of thumb, although some services seed thin lawns at the full rate. Nitrogen should not exceed about 1 lb per 1,000 ft² per application (Penn State starter guidance 0.5–1 lb), so larger seasonal totals are split into several applications.

## Data Sources

- Penn State Extension – Lawn Establishment (seeding rates and starter fertilizer) — https://extension.psu.edu/lawn-establishment (reference, retrieved 2026-09-24)
- UF/IFAS Extension ENH-03 – Establishing Your Florida Lawn (warm-season seeding rates) — https://edis.ifas.ufl.edu/publication/LH013 (reference, retrieved 2026-09-24)

Data freshness: `static`. Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output.

## API

- `GET https://tttkmbb.com/api/v1/calculate/lawn-seed-fertilizer?area=…&grass_type=…`
- `POST https://tttkmbb.com/api/v1/calculate/lawn-seed-fertilizer` with JSON body `{"inputs": {…}}`
- Response: unified envelope (`success`, `request`, `result.values`, `result.units`, `sources`, `freshness`, `timestamp`, `next_actions`, `links`); see https://tttkmbb.com/docs/response-format.md
- Schema: https://tttkmbb.com/api/v1/calculators/lawn-seed-fertilizer · OpenAPI operationId `estimate_lawn_seed_and_fertilizer` in https://tttkmbb.com/openapi.json
- Authentication: none. Rate limit: fair use, see https://tttkmbb.com/docs/rate-limits.md.

## MCP

- Server: `https://tttkmbb.com/mcp` (Streamable HTTP, JSON-RPC 2.0, no auth)
- Tool:  `run_calculator` with `{"calculator_id": "lawn-seed-fertilizer", "inputs": {…}}`

## Example

- 5,000 ft² new tall fescue lawn, 24-0-4 fertilizer: inputs `{"area":5000,"area_unit":"ft2","grass_type":"tall_fescue","seeding":"new_lawn","fertilizer_n_percent":24,"target_n_lb_per_1000ft2":1}` → `{"area_ft2":5000,"seed_rate_lb_per_1000ft2":7,"seed_lb":35,"seed_kg":15.88,"fertilizer_rate_lb_per_1000ft2":4.17,"fertilizer_lb":20.8,"fertilizer_kg":9.45,"nitrogen_lb":5}`
- 400 m² bluegrass overseeding, 20-5-10 at 0.75 lb N: inputs `{"area":400,"area_unit":"m2","grass_type":"kentucky_bluegrass","seeding":"overseed","fertilizer_n_percent":20,"target_n_lb_per_1000ft2":0.75}` → `{"area_ft2":4306,"seed_rate_lb_per_1000ft2":1.25,"seed_lb":5.4,"seed_kg":2.44,"fertilizer_rate_lb_per_1000ft2":3.75,"fertilizer_lb":16.1,"fertilizer_kg":7.32}`

```
GET https://tttkmbb.com/api/v1/calculate/lawn-seed-fertilizer?area=5000&area_unit=ft2&grass_type=tall_fescue&seeding=new_lawn&fertilizer_n_percent=24&target_n_lb_per_1000ft2=1
```

## Limitations

You are laying sod or turf rolls, need a soil-test-based lime or phosphorus recommendation, or want spacing for individual plants (use plant-spacing). New-lawn rates are the midpoints of the extension ranges (Penn State for cool-season species, UF/IFAS for warm-season species); overseeding uses half the rate as a rule of thumb, although some services seed thin lawns at the full rate. Nitrogen should not exceed about 1 lb per 1,000 ft² per application (Penn State starter guidance 0.5–1 lb), so larger seasonal totals are split into several applications. All values are computed from the formula above; no measurement or live data is involved.

## FAQ

**Why is the seeding rate so different between species?**

Seed size: Kentucky bluegrass has about 2 million seeds per pound, tall fescue about 230,000, so fescue needs far more weight to reach the same 15–20 seeds per square inch.

**How do I convert a 20-5-10 bag?**

The first number is the percentage of nitrogen by weight: 20 % means 5 lb of product per pound of nitrogen, so 1 lb N per 1,000 ft² needs 5 lb of that fertilizer per 1,000 ft².

**Should new seed get fertilizer at all?**

Cool-season lawns benefit from a starter fertilizer at 0.5–1 lb N per 1,000 ft² worked into the seedbed; Florida guidance for warm-season grass is to wait until the lawn is fully covered before adding nitrogen.

## Related

- [Area Converter](https://tttkmbb.com/conversion/area.md) — Convert the lawn area between square feet and square metres.
- [Plant Spacing Calculator](https://tttkmbb.com/everyday/plant-spacing.md) — Plant counts for beds and borders.
- [Gravel Calculator](https://tttkmbb.com/construction/gravel.md) — Aggregate for paths around the lawn.