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)^(19/24), 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

Name: Rock Fragmentation Size Estimator
Availability: InStock
Author: Nham Vu

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)^(19/24)

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