To calculate how much top dressing you need, you first need to measure the size of your lawn. For my professional lawn renovations I tend to use Google Earth to measure the area of a lawn. This tends to give a fairly accurate result, however, I’ll always validate the measurement by pacing the lawn and making sure it roughly measures up on site.
Once you have the lawn area in square metres, the amount of top dressing required depends on how heavily you want to spread it and how uneven the lawn is. More uneven lawns will use a lot more top dressing where it fills in the low areas.
Quick Answer: How much Top Dressing Do You Need?
For my professional lawn renovations, I typically order 10kg per m2 which usually leaves me with some to spare. If a lawn is reasonably flat or I only want to dress it lightly, I’ll use about 7.5kg per m2 which is about 5mm depth.
The top dressing I buy is either in 25kg bags or 850kg bulk bags. So I’ll typically order three to four 25kg bags per 10m2, or a bulk bag per 100m2.
If there is significantly levelling of larger holes and dips then I’ll fill them with topsoil before top dressing.
For a 5mm depth: Lawn area (m²) × 7.5 (kg) = kg/m2.
Example: 100m² × 7.5kg = 750kg. So 30 x 25kg bags or 1 x 850kg bulk bag.
Shopping for a levelling Rake? Compare: 43 x 25 cm compact rake · GiantexUK 46-inch levelling rake
Top-dressing quantities for common lawn sizes
The table gives approximate calculated amount of top dressing required to satisfy differing depths before any allowance for unevenness or material left over. Choose a depth suited to your grass and purpose first; a deeper depth is not automatically a better treatment.
| Lawn area | 3mm | 5mm | 7mm |
|---|---|---|---|
| 50m² | 225 kg | 375 kg | 525 kg |
| 100m² | 450 kg | 750 kg | 1,050 kg |
| 200m² | 900 kg | 1,500 kg | 2,100 kg |
| 500m² | 2,250 kg | 3,750 kg | 5,250 kg |
How to measure an irregular lawn
Divide the grass into simple rectangles and triangles, calculate each area, then add them together. A rectangle is length × width; a triangle is base × height ÷ 2. Subtract beds, paths and other areas you will not dress.
For a lawn made up of a 10m × 6m rectangle and a triangle with a 6m base and 4m height, the total is 60 + 12 = 72m². At an illustrative 5mm depth, the order volume is 540kg before rounding to available packs.
If you only intend to treat a worn section, measure that section. Buying for the entire garden when only a few dips need attention can multiply the cost unnecessarily.
How many bags should you buy?
Divide the required kg by the kg stated on each bag and round up to a whole bag. For 245 kg in 25 kg bags, 245 ÷ 25 = 9.8, so you need ten bags. That supplies 250 kg, leaving a 5 kg margin.
Do not then add another arbitrary percentage without considering whether that rounding already covers the uncertainty. For a highly uneven surface, remeasure the sections.
I’ve documented my approximate order quantities when ordering for a job. I’m usually ordering for a full lawn renovation where I’ve aerated and I’ll be losing a lot of dressing down the holes so I order for a depth from 5mm to just short of 7mm.
| Lawn area | kg | 25 kg bags | 850kg bulk bags |
|---|---|---|---|
| 50m² | 375 – 525 | 15 – 21 | 0.5 |
| 100m² | 750 – 1,050 | 30 – 42 | 1 |
| 200m² | 500 – 2,100 | 60 – 84 | 2 – 2.5 |
| 500m² | 3,750 – 5,250 | 150 -210 | 4.5 – 6 |
Why a 25kg bag is not a 25-litre bag
Kilograms measure mass; litres measure volume. Sand, soil and compost mixtures can have different bulk densities and moisture contents. You cannot reliably substitute one unit for the other.
If the supplier sells only by litres, ask for the product’s bulk density or stated coverage at a known depth. With bulk density in kg/m³, multiply your required m³ by that density to estimate kilograms. Without that information, a confident litre figure would be guesswork.
Likewise, “bulk bag” is a packaging description. Check the supplier’s declared weight or volume rather than assuming every bag contains one cubic metre.
How deep should top dressing be?
The calculation cannot choose the treatment for you. A light surface dressing, filling aeration holes and correcting isolated dips have different requirements. Avoid covering the existing grass completely or trying to repair a deep depression with a blanket layer over the whole lawn.
The RHS autumn lawn-care guide discusses applying a suitable dressing after lawn care, including working material into aeration holes. Its weight-based guidance relates to that treatment and mixture; it is not a universal conversion for every bag sold as top dressing.
What equipment is worth buying?
For repeat top-dressing work I use levelling rakes to work the top dressing across the surface. Choose the head size around the area and your ability to move loaded material, using our rake-size guide and lawn levelling rake buying guide.
If you’re looking to spread compost over the top then you need to be looking at a mesh compost spreader which can distribute compatible fine material. Check out my article looking at the best top dressing spreaders.
When using a spreader its always worth remembering that lumpy, wet or unsuitable mixtures may not pass through it well. I always try to ensure my top dressings are dry.
Before you place the order
- Confirm the treated area and purpose, rather than just total garden size.
- Check the mixture, screening and units on the supplier’s listing.
- Compare the delivered cost for equivalent quantities.
- Arrange a practical drop-off point; moving hundreds of litres by hand adds work.
- Have spreading equipment and a suitable weather window ready.
How much top dressing do I need for 100m²?
At 3mm, 450 kg; at 5mm, 750 kg; at 7mm, 1,050 kg. Those are mathematical quantities, not blanket depth recommendations. If only part of the lawn needs dressing, calculate that part separately.
Sources and buying checks
Specifications and product listings checked on 18 September 2026. Manufacturers can change products and retailers may sell different variants; check the exact listing before ordering.
