Advanced Newmark Influence Chart Calculator

Case	q (kPa)	n	iu	I = n × iu	Δσz = q × I (kPa)
Case A	120.000	18	0.005	0.090	10.800
Case B	150.000	32	0.005	0.160	24.000
Case C	200.000	44	0.005	0.220	44.000
Case D	250.000	56	0.005	0.280	70.000

Formula Used

1) Total influence factor
I = n × iu

2) Vertical stress increase at depth
Δσz = qf × I

3) Factored load
qf = q × load factor

4) Total vertical stress
σtotal = σ0 + Δσz

5) Chart coverage percentage
Coverage % = (n / 200) × 100

Where n is the number of covered chart units, iu is the influence value per unit, q is the applied surface pressure, and σ0 is the existing overburden stress. For a standard 200-unit chart, iu = 0.005.

How to Use This Calculator

Choose a case name for your footing, tank, slab, or embankment load.
Enter the uniform applied load in kPa.
Apply a load factor if you want a factored design check.
Count how many Newmark chart units are covered after scaling the loaded area to the chosen depth.
Use 0.005 for each block when working with a standard 200-unit chart.
Enter depth, footing width, and footing length for reference ratios.
Add overburden stress if you want total vertical stress instead of only the increase.
Press calculate to show the result above the form and the graph below it.
Download CSV or PDF summaries for reporting, checking, or documentation.

FAQs

1) What does the Newmark influence chart estimate?

It estimates the vertical stress increase at a point in soil below a loaded area. The method converts the counted influence units into an influence factor, then multiplies that factor by the applied surface pressure.

2) Why is 0.005 used as the default unit value?

Many standard Newmark charts divide the influence area into 200 equal units. Each covered unit contributes 1/200 of total influence, so the default block value becomes 0.005.

3) Does depth directly change the formula here?

Not after the chart count is completed. Depth is used earlier while scaling the loaded area on the chart. Once units are counted, the stress increase comes from load times influence factor.

4) What if my chart uses a different number of units?

Change the unit influence value to match your chart. For example, if each block represents 0.0025 instead of 0.005, enter that value before calculating the stress increase.

5) Why are z/B and z/L shown?

They help you understand the relative depth compared with foundation dimensions. These ratios are useful for engineering review, comparison between cases, and quick documentation of the stress evaluation point.

6) Can this calculator be used for irregular loaded areas?

Yes. That is one of the main advantages of the chart method. Trace the irregular area on the scaled chart, count the covered units, and then enter the unit count here.

7) What is the difference between stress increase and total stress?

Stress increase is only the added stress caused by the external load. Total stress includes any existing overburden stress you entered, so it represents the combined vertical stress at depth.

8) Is this calculator suitable for settlement design alone?

It helps estimate stress distribution, which is an input for settlement work. Settlement calculations still require soil compressibility, layer thickness, modulus, or consolidation parameters depending on the analysis method.

Engineering note: verify manual chart counting, footing geometry, and unit influence assumptions before using results in design documents.