Calculator Inputs
Enter field values. The tool estimates mean fragment size and passing curve using common fragmentation models. Use project specs for final design.
Example data table
This example shows typical inputs and the type of outputs you may see. Your site conditions will change results.
| Burden (m) | Spacing (m) | Bench (m) | Dia (mm) | Stemming (m) | Density (kg/m³) | RWS (%) | A | Estimated X50 (mm) | Estimated P80 (mm) |
|---|---|---|---|---|---|---|---|---|---|
| 2.8 | 3.2 | 10 | 115 | 3.0 | 1100 | 100 | 6.0 | ~160 | ~280 |
| 3.0 | 3.4 | 12 | 127 | 3.2 | 1200 | 105 | 5.5 | ~150 | ~260 |
Formula used
Step 1: Volume and charge per hole
V = Burden × Spacing × BenchHeight(m³ per hole)HoleLength = BenchHeight + Subdrill(m)ChargeLength = HoleLength − Stemming(m, auto if left blank)ChargeMass Q = (π × D² / 4) × ChargeLength × Density(kg)PowderFactor = Q / V(kg/m³)
Step 2: Mean fragment size (Kuznetsov-style)
X50(cm) = A × (V/Q)^0.8 × Q^0.167 × (115/RWS)^0.19, then convert to millimetres.
The rock factor A reflects structure, hardness, and jointing.
Step 3: Size distribution (Rosin–Rammler)
Passing fraction at size x:
P(x)= 1 − exp( −(x/Xc)^n ).
We compute Xc from X50:
Xc = X50 / (ln2)^(1/n).
This is an estimation framework. Field trials and site controls remain essential.
How to use this calculator
- Enter burden, spacing, and bench height from your drilling pattern.
- Provide hole diameter, stemming, and subdrill based on design.
- Leave charge length blank to auto-calculate, or set it manually.
- Input explosive density and RWS from your product data.
- Set rock factor A using site observations and records.
- Choose auto or manual uniformity index n, then set sieve sizes.
- Press Calculate to view results above the form.
- Use Download CSV or Download PDF for reporting.
Professional article
Fragmentation control sits at the centre of productive drilling and blasting. When fragments are too coarse, secondary breakage, oversized handling, and crusher choke points add delays, fuel use, and equipment wear. When fragments are too fine, vibration, dust generation, and material losses can rise. A consistent estimation step helps engineers compare pattern options quickly before committing equipment, consumables, and time.
This calculator combines a mean size estimate with a size distribution curve. The mean size (X50) is the fragment size where 50% of the material is finer and 50% is coarser. The Rosin–Rammler model then translates X50 and the uniformity index n into passing percentages at the sieve sizes you choose. The result is a practical view of what fraction is likely below a given size, which supports decisions for diggability, loading rate, and downstream plant performance.
Use the inputs as a disciplined checklist. Burden and spacing define the rock volume assigned to each hole. Bench height and subdrill set drilled length and influence toe breakage and floor control. Stemming controls confinement and can shift energy toward breakage rather than venting. Hole diameter, charge length, and explosive density determine explosive mass per hole, while RWS scales relative energy output. The rock factor A represents the combined influence of rock mass structure, jointing, and hardness. Start with a value from site history, then tune it using measured fragmentation from a few representative blasts.
Example data: burden 2.8 m, spacing 3.2 m, bench height 10 m, subdrill 1.0 m, hole diameter 115 mm, stemming 3.0 m, explosive density 1100 kg/m³, RWS 100, and A 6.0. With charge length left blank, the tool auto-calculates charge length as (10 + 1 − 3) = 8.0 m. After you calculate, review X50, P20, and P80, then interpret passing percentages at sieve sizes such as 50, 150, 300, and 600 mm. If your target is a lower P80, typical levers include modestly tightening burden or spacing, improving coupling, adjusting stemming within safe limits, or revisiting delay timing and initiation sequence. Always verify changes with your blasting engineer and applicable regulations.
Treat the outputs as planning numbers, not guarantees. Validate with field measurements such as image analysis, belt sampling, or sieve checks. Account for geology changes across the bench, document outcomes, and build a local calibration set so future designs start closer to the desired fragmentation window. If you have measured distributions, switch to manual n and match it to your data. Use results to discuss targets with drilling, loading, and plant teams.
FAQs
What does X50 represent?
X50 is the median fragment size. About half the blasted material is expected to be smaller than X50 and half larger, based on the selected distribution model.
How do I select the rock factor A?
Use site history first, then calibrate. Hard, massive rock with few joints usually needs a higher A, while fractured or weathered rock tends to use a lower A. Adjust A until estimates align with measured fragmentation.
When should I use manual uniformity index n?
Use manual n when you have reliable sieve or image-analysis data from similar blasts. Set n to match the observed curve shape, then keep it consistent while you test pattern changes.
Why does stemming influence fragmentation?
Stemming increases confinement near the collar, reducing early venting. Better confinement generally improves energy use in the burden and can reduce oversize, but excessive stemming may increase toe problems or backbreak.
Can I compare different explosive products?
Yes, if you input the correct density and a reasonable RWS for each product. Keep geometry and rock factor consistent so the comparison reflects explosive energy differences rather than pattern changes.
What sieve sizes should I enter?
Choose sizes that match your operational controls: crusher opening, target top size, or screen decks. Adding one fine, one mid, and two coarse sizes often gives a useful picture of the passing curve.
Are these results guaranteed for field blasting?
No. This is an estimating tool. Geology, confinement, initiation timing, and charging practice can shift fragmentation significantly. Validate with field measurements and follow your project’s blasting procedures.