How much does stump grinding cost?

Rather than pricing purely on diameter, our model asks a more useful question: how much work is this particular stump likely to require? Each input feeds into the next, ending in a single estimate.

1. Stump diameter
2. Predicted grinding time
3. Tree species adjustment
4. Access
5. Site conditions
6. Machine + operator + attendance
7. Final estimate

Crucially, grinding time does not increase in a straight line with diameter. Our current Standard Access baseline formula is:

Where T is the predicted grinding time in minutes and D is the stump diameter in centimetres. Because the exponent is greater than 1, larger stumps become disproportionately more time-consuming.

These are predicted grinding minutes before any species adjustment — not the total time on site.

Why the exponent is 1.7601

The shape of the curve was derived from published stump grinder performance benchmark data — approximately:

A power-law fit to that performance data produced an exponent of approximately 1.7601. This does not make the model perfect — it gives us a rational starting curve that we can calibrate against our own real-world job data over time.

We're transparent about this: Janka hardness measures resistance to indentation. It is not a direct measurement of stump-grinding cutting resistance. Actual performance is also affected by wood density, moisture, grain, decay, root structure, soil contamination and cutter condition. But Janka gives us an objective, repeatable starting point.

Where J is the species' Janka value and 2000 N is our reference baseline. We deliberately use the square root to dampen the effect of hardness: a species with twice the Janka hardness is not automatically assumed to take twice as long to grind.

Species examples

The calculator contains a much larger species database. These are working estimation inputs, not claims that Janka hardness perfectly predicts grinding:

Combining diameter and species

Take a 50cm stump. The baseline grinding time is:

Apply the species factor and the same diameter gives different times:

Same diameter, different species, different predicted grinding time.

You can see restricted access in practice in our tight-access stump grinding work.

• Preparing / exposing the stump
• Stones and rocks
• Repositioning equipment
• Protection boards
• Working around walls, fences and paving
• Chainsaw preparation
• Raking grindings
• General preparation and tidying

Where T is total predicted grinding minutes and C is the site-condition multiplier (1.50 / 1.75 / 2.00).

Why £100 attendance?

Even a very small stump requires travel, transporting specialist machinery, unloading, access and setup, loading again and travelling away. That fixed £100 happens once per visit — which is exactly why a tiny stump can't simply be priced by multiplying its diameter by £3.

Why £250/hour machine time?

This is a commercial machine selling rate, not simply the cost of fuel. It contributes towards machinery investment, depreciation, fuel, grinding teeth, belts, filters, servicing, repairs, maintenance, transport, downtime and eventual replacement.

Why £100/hour operator time?

Productive labour is more than the minutes spent physically grinding. If the operator is preparing the stump, repositioning equipment, digging around an obstruction or clearing the job, they're still working. The productive operator rate is £100/hour.

50cm stump, species Unknown / Not sure, Standard access, Normal conditions.

1. 1

   Diameter

   30 × (0.5)^1.7601

   ≈ 8.86 minutes

2. 2

   Species

   Unknown = 3000 N → √(3000 / 2000) = 1.2247
   8.86 × 1.2247

   ≈ 10.85 grinding minutes

3. 3

   Machine

   10.85 / 60 × £250

   ≈ £45.21

4. 4

   Operator

   10.85 × 1.50 = 16.28 productive minutes
   16.28 / 60 × £100

   ≈ £27.13

5. 5

   Attendance

   Fixed, once per visit

   £100

Final price rounding

We don't quote awkward prices like £172.34. The calculator always rounds the final result up to the nearest £5.

Estimated time on site

Grinding time isn't the same as total time on site. Our scheduling model adds a fixed 20-minute setup/load allowance, then rounds up to the next 15-minute block:

20 + (10.85 × 1.50) ≈ 36.28 minutes → rounds up to 45 minutes

The 20-minute scheduling allowance isn't charged as a separate labour item — attendance is already represented by the fixed £100 visit component.

This part matters. We never simply combine stump diameters before applying the grinding-time curve. Three 50cm stumps are not calculated as one 150cm stump — because the diameter/time relationship is nonlinear, that would incorrectly treat three moderate stumps as one enormous stump.

Each stump can also have its own species — for example a 50cm Leylandii, a 70cm Oak and a 35cm Unknown each get their own diameter/species calculation before the grinding times are combined.

Why multiple stumps are better value

The £100 attendance component occurs only once per visit. If several stumps are completed while we're already at the property, the cost of attending is shared, so the effective £/cm naturally falls. This isn't an arbitrary bulk discount — it's the natural result of completing several stumps efficiently during one visit.

Multiple-stump worked example

3 × 50cm Unknown stumps, Standard access, Normal conditions. Each predicted grinding time is ≈ 10.85 minutes.

1. 1

   Total grinding time

   10.85 × 3

   ≈ 32.55 minutes

2. 2

   Machine

   32.55 / 60 × £250

   ≈ £135.63

3. 3

   Operator

   32.55 × 1.50 = 48.83 productive minutes
   48.83 / 60 × £100

   ≈ £81.38

4. 4

   Attendance

   Once

   £100

Multi-stump saving benchmark

The calculator can show how the estimate compares with the simple benchmark rate (£3/cm Standard, £5/cm Restricted). For the example above:

The benchmark does not influence the actual price. The saving is only displayed when there are two or more stumps and the calculated estimate is below the relevant benchmark. Restricted Access uses the £5/cm comparison.

• Standard grinding depth

  Approximately 8 inches / 20cm below ground level.

• Wood chips / grindings

  Normally raked back into the hole. Removal can be quoted separately.

• Surface roots

  Not automatically included in the calculator. If particular roots need removing for paving, landscaping or another project, they can be assessed separately.

Stump grinding does not mean excavating the entire underground root system — it removes the stump and main root mass to the depth above.

This is an estimation model. A stump is a natural object in an uncontrolled environment, and actual performance can be affected by things the calculator simply cannot see:

• Moisture
• Decay
• Unusual root structure
• Soil and stones
• Concrete
• Embedded metal
• Old fencing
• Underground services
• Stump height
• Cutter condition
• Exact access
• Unusual site constraints

And, as above, Janka hardness is a proxy — not a direct measure of stump-grinder cutting resistance. So the calculator produces an estimate, and we ask you to send photos afterwards so we can confirm the quote.

Why we built the model

We could simply charge a flat £3/cm. That would be easier — but it would imply that every stump of the same diameter is the same job. Our approach instead asks: how much work is this particular stump likely to require?

As we complete real jobs, we compare predicted grinding time against actual grinding time, predicted site time against actual site time, and predicted workload against actual workload. Real-world data then refines the diameter curve, baseline grinding times, species adjustments, site-condition allowances and restricted-access performance — so the calculator improves as our job dataset grows.

The current Standard Access mathematical engine behind the estimate, in one place: