Lawn Seed Calculator
Calculate how much grass seed to sow for a new lawn or a repair.
Last updated · View algorithm, constants and default inputs (JSON)
About this calculator
Estimate seed mass from lawn area, the selected seed type and project factor, plus waste. Rates are model assumptions; check the seed label for the cultivar, whether you are starting or overseeding, and local conditions. Five-pound bag count rounds up.
Worked example
calculated with the default values below
Lawn length 50 ft · Lawn width 30 ft · Project type New lawn · Grass type Tall fescue (6 lb/1000 sq ft new) · Waste allowance 10 % Lawn area 1,500 sq ft · Lawn area in thousands 1.500 x1000 sq ft · Seed needed 9.90 lb · Seed needed 4.49 kg · 5 lb bags needed 2
General background references
Disclaimer
These are general gardening estimates. Planting windows, growth, water and nutrient needs vary by place and plant. Check local extension guidance and product labels before acting on an estimate.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
seed_lb=L×W÷1000×r×p×(1+w÷100); bags=ceil(seed_lb÷5)
- L,W
- lawn dimensions (ft)
- r
- fixed seed-type rate (lb/1,000 sq ft)
- p
- project factor
- w
- waste (%)
Rates and project multipliers are planning assumptions; follow the selected seed product label. Five-pound bag count rounds up.
Frequently asked questions
Why does a new lawn need twice the seed of overseeding?
Seeding rates differ sharply by project: a new lawn takes the full rate while overseeding uses half, and repair 1.2 times. With fescue at 6 lb per 1,000 sq ft on a 50 by 30 foot, 1,500 sq ft, new lawn plus 10% waste, the tool calls for 9.9 lb, about 4.5 kg in two 5-lb bags; the same area overseeded would need only 5 lb.