How Much Grass Seed
Do I Need?

For most UK lawns using a ryegrass or fescue mix, the standard rate is 35–50g per m² for a new lawn from bare ground. For overseeding an existing lawn, use 20–25g per m². Specialist grass types like pure bent grass use a much lower rate of just 8–10g per m² due to their tiny seed size.

For a new 100m² lawn using a standard ryegrass mix at 35g/m², you need 3,500g — or 3.5kg of seed. At the higher rate of 50g/m², you would need 5kg. For overseeding the same 100m² at 20g/m², you need just 2kg. Always buy slightly more than the calculated amount to cover wastage on edges and uneven ground.

For a new 200m² lawn at the standard 35g/m² rate, you need 7kg of seed. At the denser rate of 50g/m², you need 10kg. For overseeding 200m² at 25g/m², you need 5kg. For fine bent grass or fescue mixes, rates are lower — 35g/m² is the typical starting point for all ornamental UK grass mixes.

A new lawn needs roughly double the seed rate of overseeding. With bare ground, seed has no competition and needs to establish full coverage from scratch, so more seed is needed. Overseeding patches or thinning turf requires less seed because existing grass fills in gaps over time. Using the full new-lawn rate when overseeding wastes money and can suffocate existing grass.

For a rectangular lawn, simply multiply the length (in metres) by the width (in metres). For example, a lawn that is 12m long and 8m wide = 96m². For L-shaped or irregular lawns, divide the area into separate rectangles, calculate each section, and add them together. For circular lawns, use the formula π × radius² (3.14159 × radius × radius).

Yes. To convert square feet to square metres, divide by 10.764. For example, 1,000 sq ft ÷ 10.764 = approximately 92.9m². UK seed rates are always given in grams per m², so converting your measurements to metric first will give you the most accurate results. Our calculator above handles this conversion automatically when you select sq ft as your unit.

Always stick as close as possible to the recommended rate. Too little seed results in thin, patchy coverage with gaps that weeds will fill. Too much seed creates overcrowded seedlings that compete intensely with each other for light and water, leading to weak grass that is vulnerable to disease. Over-sowing is one of the most common mistakes UK gardeners make.

The two ideal windows for sowing grass seed in the UK are mid-spring (April to May) and early autumn (August to September). Autumn is generally considered the best time, as soil temperatures are warm from summer, rainfall is more reliable, and weed competition is lower. Avoid sowing during summer drought, frost periods, or waterlogged winter conditions.

Once you know your total seed requirement in kg, simply divide by the bag size. For example, if you need 3.5kg and bags come in 1kg, you need 4 bags (always round up, never down). Our calculator above gives you an instant bag count for 500g, 1kg, and 5kg bag sizes. Buying in larger bags is almost always more cost-effective per kg.

For a family lawn that needs to withstand children, pets, and regular foot traffic, a hard-wearing perennial ryegrass mix (or a dwarf ryegrass and fescue blend) is the best choice. Look for mixes containing modern dwarf ryegrass cultivars, which are denser, more disease-resistant, and slower-growing than older varieties. Avoid fine fescue or bent grass mixes, which are ornamental and cannot handle heavy use.

Perennial ryegrass germinates in 7–14 days in ideal conditions (soil temp above 10°C, consistent moisture). Fescue mixes take 14–21 days. Bent grass can take 14–28 days. Germination will be slower in cold spring conditions and faster in warm, moist autumn soil. The first cut should be made once grass reaches approximately 5–7cm, with the mower set to its highest setting.

The seed quantity (g/m²) is the same — approximately 35g/m² for a new shaded lawn — but the grass species matters enormously. For shaded areas, choose a seed mix specifically designed for shade, which will be high in creeping red fescue and rough-stalked meadow grass (Poa trivialis), both of which are tolerant of low light. Do not use a standard ryegrass mix in deep shade, as it will fail.

35g per m² is a medium-density coverage. When applied correctly, you should be able to just see the soil through the seed when looking at the ground level after sowing — not a thick blanket, but a visible layer. If you cannot see any soil at all, you have over-seeded. A hand-held spreader or rotary spreader makes it much easier to apply evenly at this rate than broadcasting by hand.

Yes, the formula is the same regardless of scale: Area (m²) × Rate (g/m²) ÷ 1,000 = kg required. For a standard football pitch (~6,000m²) at 35g/m², you need 210kg of seed. For professional sports applications, always consult a qualified groundsman or the Sports Turf Research Institute (STRI) for species selection and site-specific sowing rates.

DEFRA (Department for Environment, Food & Rural Affairs) certified seed has been independently tested and verified for purity, germination rate, and species accuracy. It means you are guaranteed to receive the grass type shown on the label with a minimum germination percentage (typically 80–95%). Non-certified cheap seed may contain weed seed, low-viability old seed, or misidentified species — all leading to poor lawn results.