Grit Salt Calculator (UK): grams per square metre and 25 kg bags

How much grit salt per m2?

Spread 10 g/m² for a precautionary run against frost and light snow, 20 g/m² where frost follows rain, and 20 to 40 g/m² when heavy snow is expected. Those are Argyll and Bute Council’s published rates. A 25 kg bag covers 2,500 m² at 10 g/m² and 625 m² at 40 g/m². For a car park, area in m² times the rate, divided by 1,000, is the salt in kilograms for one run.

That is the whole of the arithmetic. What changes the answer is the rate, which is why the calculator above makes you pick a treatment first, shows the rate in use on every run, and lets you replace it with your own. The rest of this page is about where those rates come from and what they do and do not cover.

UK spread rates as councils publish them

UK councils publish their winter service rates in grams per square metre. The figures below are quoted from the documents cited at the foot of this page, retrieved on 17 October 2026.

Three things are worth reading into that table. First, these are one council’s policy, a second council’s summary and one buyer’s tender; none of them is a national standard, and a private site is not bound by any of them. Second, the heavy-snow rate is a range on purpose: Argyll and Bute sets it “according to the anticipated severity of snowfall and confidence level of the forecast”, so the calculator shows both ends and counts bags at the top. Third, the hospital tender asks bidders to price every gritting run at 20 g/m² and at 30 g/m², for mechanical and hand gritting alike. It does not tie either rate to a weather condition, so the calculator reports both and does not invent the link.

The US edition of this tool, the de-icing salt calculator, works the same job in pounds per 1,000 sq ft and 50 lb bags against US agency and supplier tables. Those rates are not converted onto this page, because they come from a different system with a different basis, and a converted US number is not a UK council rate.

Grit, rock salt and white salt: what you are buying

“Grit” means two things in UK winter work, and the difference matters for the order. Clackmannanshire Council calls what it spreads on its roads “grit (or crushed rock salt)”. The same council fills its roadside bins with “a 50/50 mixture of grit and rock salt”, where grit is an abrasive that gives grip and the salt does the melting. A bag of grit salt for spreading is normally rock salt. A bin fill may be half that.

Brown rock salt and white de-icing salt are both specified in practice. The NHS tender accepts “either high quality white de-icing salt or rock salt conforming to BS 3247 or EN equivalent”. One UK merchant states that the two “are equally as effective at melting ice”, and draws the line at residue: brown rock salt “does leave a slight residue behind” that is walked indoors, white salt does not. The same merchant lists car parks among rock salt’s usual users and suggests white salt where there is a lot of foot traffic in and out of buildings. The calculator uses one rate for both, because no source cited here gives a different one.

Bags, tonnes and runs

Salt is bought by the bag or by the tonne and spent by the run. The calculator counts both ways:

• Bags round up, because you cannot buy part of one. The 25 kg default is a starting point; set the weight your supplier prints on the bag.
• Tonnes stay continuous, because loose salt is sold by weight.
• Runs are every pass you make, precautionary or re-treatment. In heavy snow Clackmannanshire treats its main roads “continuously, with successive grits meaning the use of grit is far higher”, so a cold week can be many runs.

A worked example, the same one the calculator’s tests check: a 1,200 m² car park at the tender’s 20 and 30 g/m² is 24 to 36 kg a run, or two 25 kg bags at the top rate. Forty runs at the top rate is 1,440 kg, which is 58 bags or 1.44 tonnes. The forty is an example input. Use the run count your contract states or your own records show.

Where rock salt should not go

Two flags in the calculator come from the sources, not from caution for its own sake.

Metal decking. The NHS tender tells bidders “to avoid products based on sodium chloride (rock salt) because they are chemically aggressive/corrosive to metal” on car park decking, and points to potassium acetate products instead. Tick the decking box and the calculator warns you; leave the decked area out of the salt figure and price it from that product’s label.

Very cold surfaces and settled snow. Clackmannanshire’s grit bin guidance says salt “becomes increasingly less effective and eventually will not work at all” once the surface falls below −5 °C. Its road guidance adds that grit “will generally not stop the snow from settling, unless the snowfall is very light”, and on footways Argyll and Bute makes physical clearance the priority in all snowfall, with sand or grit spread afterwards for traction. Clear first, then spread.

The national guidance, and why its numbers are not here

Clackmannanshire says it follows “national guidance”. Two documents that sit behind UK council rates, the National Winter Service Research Group’s guidance on spread rates for precautionary salting and a North Yorkshire County Council report on lowering that council’s minimum rate, could not be retrieved on 17 October 2026: one returned a 403, the other refused the connection. We have not printed any figure from either, rather than repeat a number we could not check. If your client works to that guidance, its rate goes straight into the override.

From quantity to a priced job

Salt is one line in a gritting job, not the job. If the work includes snow clearance, the snow removal pricing calculator builds a per-push and seasonal price from labour, equipment, salt and margin; it was built around North American contracts, so enter your own costs and read it for structure. The terms belong in writing: the UK service contract template carries a consumer or business version with a VAT line, and the UK quotation template is where the priced run goes to the customer. The hospital tender is a useful model of what a buyer asks for: an activation temperature of 0 °C “as determined by the Met Office”, and a report for each visit showing “date, time, location, method, spread rate and Met Office temperature”. The spread rate you record there is the one this calculator sizes.