What is the Kuznetsov equation?

The Kuznetsov (1973) equation predicts the mean fragment size (x50) produced by blasting: x50 = A × (V/Q)^0.8 × Q^(1/6) × (115/RWS)^(19/30), where A is the rock factor, V is the volume of rock per hole (m³), Q is the explosive mass per hole (kg), and RWS is the relative weight strength of the explosive versus ANFO.

What rock factor A should I use?

A = 1–3 for soft, heavily jointed rock; A = 4–6 for medium-hard rock with moderate jointing; A = 7–10 for hard, sparsely jointed rock; A = 11–16 for very hard, massive rock such as granite or quartzite. Use the midpoint of each range as a starting estimate.

What is RWS and what value should I enter?

RWS (Relative Weight Strength) compares the energy of an explosive to ANFO (RWS = 100). Typical values: ANFO ≈ 100, Heavy ANFO ≈ 110–115, Bulk emulsion ≈ 115–120, Watergel ≈ 105–115. Use 115 if you are unsure, which is a common default for emulsion.

How is volume per hole (V) calculated?

V = Burden × Spacing × Bench height (all in meters). For example, a 3 m burden, 3.5 m spacing, and 10 m bench gives V = 105 m³ per hole. Enter this value in the Volume field, or use the built-in helper to compute it from burden, spacing, and bench height.

What does the output x50 mean?

x50 is the median fragment size: 50% of the blasted material by mass will be smaller than this diameter. It does not describe the full particle size distribution — use the Rosin-Rammler distribution (with the uniformity index n) to get a complete grading curve.

Is this tool accurate enough for production blasting?

The Kuznetsov equation is a widely used empirical model suitable for preliminary design and sensitivity analysis. For final production blast designs, supplement it with site-specific calibration data, image analysis of muck pile fragmentation, and geotechnical input from a qualified blast engineer.

Rock Fragmentation Size Estimator

Estimate mean rock fragment size from blasting using the Kuznetsov equation given explosive charge, rock mass factor, and hole geometry.

Explosive & Rock Parameters

Explosive charge per hole (Q, kg)

Relative Weight Strength (RWS, ANFO=100)

ANFO = 100 | Emulsion ≈ 115 | Heavy ANFO ≈ 110–115

Rock mass factor (A)

Hole Geometry — Volume per Hole

Fill burden, spacing, and bench height to compute V, or enter V directly.

Burden (m)

Spacing (m)

Bench ht. (m)

or enter directly

Volume per hole (V, m³)

Kuznetsov Equation Reference

x50 = A × (V/Q)^0.8 × Q^(1/6) × (115/RWS)^(19/30)

x50 — mean fragment size (cm)
A — rock mass factor (1–16)
V — volume of rock per hole (m³)
Q — explosive charge per hole (kg)
RWS — relative weight strength (ANFO = 100)

Source: Kuznetsov, V.M. (1973). The mean diameter of fragments formed by blasting rock. Soviet Mining Science, 9(2), 144–148.

Rock Factor A — Quick Reference

A value	Rock description
1–3	Soft, heavily jointed or friable
4–6	Medium-hard, moderate jointing
7–10	Hard, sparsely jointed
11–16	Very hard, massive (e.g., granite)

Summary

Estimate mean rock fragment size from blasting using the Kuznetsov equation given explosive charge, rock mass factor, and hole geometry.

How it works

Enter the explosive charge per hole (kg) and the volume of rock broken per hole (m³).
Set the rock mass factor A (1–16), which reflects joint spacing and hardness.
Enter the relative weight strength of the explosive (RWS) compared to ANFO (default 115 for emulsion).
The tool computes powder factor (kg/m³) and applies the Kuznetsov equation: x50 = A × (V/Q)^0.8 × Q^(1/6) × (115/RWS)^(19/30).
Review the estimated mean fragment size in centimeters and adjust inputs to meet your target grading.

Use cases

Verify blast designs meet crusher feed size specifications before drilling.
Compare fragment size outcomes for different explosive types or charge weights.
Optimize burden and spacing to reduce oversize or fines.
Quick field estimates during drill-and-blast planning for quarry or mine operations.
Academic study of blast fragmentation theory and the Kuznetsov equation.
Sensitivity analysis — see how changes in rock factor A affect fragment size.

Frequently Asked Questions

Last updated: 2026-09-20 · Reviewed by Nham Vu

Rock Fragmentation Size Estimator

Explosive & Rock Parameters

Hole Geometry — Volume per Hole

Estimated Fragmentation Result

Fragment Size Interpretation

Kuznetsov Equation Reference

Rock Factor A — Quick Reference

Summary

How it works

Use cases

Frequently Asked Questions

Rock Fragmentation Size Estimator

Use the Rock Fragmentation Size Estimator

Explosive & Rock Parameters

Hole Geometry — Volume per Hole

Estimated Fragmentation Result

Fragment Size Interpretation

Kuznetsov Equation Reference

Rock Factor A — Quick Reference

Summary

How it works

Use cases

Frequently Asked Questions