Assess foot posture with three measurements
Calculate the arch index from a footprint, navicular drop and the arch height index (AHI). Each measure is independent; enter only the ones you have, and each panel's result appears straight away.
Arch index (AI)
How to measure
- With the person standing and weight evenly on both feet, take a footprint on 1 cm grid paper using an ink pad or a wet foot.
- Draw the foot axis from the centre of the heel to the tip of the second toe; divide the print length, excluding the toes, into three equal thirds with lines perpendicular to the axis: forefoot (A), midfoot (B), rearfoot (C).
- Count the squares in each third (count a square as whole if more than half is covered) and enter the areas in cm².
For footprint width ratios (Chippaux-Smirak, Staheli), use the Foot Arch Index tool.
Navicular drop (ND)
How to measure
- With the person standing and weight evenly on both feet, place the subtalar joint in neutral so the talar head feels equal on the inner and outer sides.
- Mark the navicular tuberosity and measure its height from the floor with a ruler.
- Let the person relax into their normal stance and measure the height of the same mark again.
Arch height index (AHI)
How to measure
- Measure total foot length (back of heel to tip of the longest toe) and mark its midpoint.
- Measure the height of the dorsum of the foot from the floor at that point.
- Measure truncated foot length: from the back of the heel to the centre of the first metatarsophalangeal joint.
- Select whether the measurement was taken sitting or standing.
From the back of the heel to the centre of the first metatarsophalangeal joint.
Result
Fill in at least one panel to see a result.
Screening measurements
These values are screening measurements. Foot type classification and orthosis or insole decisions are made by a clinician together with examination, symptoms and gait. They are not a substitute for the FPI-6 or imaging, and the result is not a diagnosis.
Sources
- Cavanagh PR, Rodgers MM. The arch index: a useful measure from footprints. J Biomech. 1987;20(5):547–551. doi:10.1016/0021-9290(87)90255-7
- Menz HB, et al. Visual categorisation of the arch index: a simplified measure of foot posture in older people. J Foot Ankle Res. 2012;5:10. doi:10.1186/1757-1146-5-10
- Brody DM. Techniques in the evaluation and treatment of the injured runner. Orthop Clin North Am. 1982;13(3):541–558.
- Mueller MJ, Host JV, Norton BJ. Navicular drop as a composite measure of excessive pronation. J Am Podiatr Med Assoc. 1993;83(4):198–202. doi:10.7547/87507315-83-4-198
- Vinicombe A, Raspovic A, Menz HB. Reliability of navicular displacement measurement as a clinical indicator of foot posture. J Am Podiatr Med Assoc. 2001;91(5):262–268. doi:10.7547/87507315-91-5-262
- Williams DS, McClay IS. Measurements used to characterize the foot and the medial longitudinal arch: reliability and validity. Phys Ther. 2000;80(9):864–871.
- Butler RJ, et al. Arch height index measurement system: establishment of reliability and normative values. J Am Podiatr Med Assoc. 2008;98(2):102–106. doi:10.7547/0980102
- Menz HB, Munteanu SE. Validity of 3 clinical techniques for the measurement of static foot posture in older people. J Orthop Sports Phys Ther. 2005;35(8):479–486. doi:10.2519/jospt.2005.35.8.479
- Redmond AC, Crosbie J, Ouvrier RA. Development and validation of a novel rating system for scoring standing foot posture: the Foot Posture Index. Clin Biomech. 2006;21(1):89–98. doi:10.1016/j.clinbiomech.2005.08.002
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Frequently asked questions
What is the Foot Posture Index (FPI-6) and why isn't it on this page?
The FPI-6 is an observational tool that scores six criteria in standing (talar head palpation, supra- and infra-lateral malleolar curvature, calcaneal frontal plane position, prominence in the talonavicular region, height and congruence of the medial longitudinal arch, and abduction/adduction of the forefoot on the rearfoot) (Redmond et al., Clin Biomech 2006). Its manual and scoring materials are licensed by the University of Leeds for commercial use. This page therefore offers free, formula-based measures instead; clinicians can use the FPI-6 under licence.
How is navicular drop measured and how much is a lot?
With the person standing and weight evenly on both feet, the subtalar joint is placed in neutral, the navicular tuberosity is marked and its height from the floor is measured; the person then relaxes into their normal stance and the height is measured again. The difference is the navicular drop. Mueller et al. (1993) suggested 10 mm and Brody (1982) 15 mm as upper limits; these are suggestions, not validated cut-offs. Reliability is moderate, with a measurement error of about ±1.5–3.5 mm (Vinicombe et al. 2001).
What is the arch index and how are the bands defined?
The arch index (Cavanagh and Rodgers, J Biomech 1987) divides the footprint, excluding the toes, into three equal thirds along the foot axis and takes the midfoot area as a proportion of the total (AI = B ÷ (A + B + C)). As reported by Menz et al. (2012), below 0.21 is a high arch, 0.21–0.26 normal and above 0.26 a low (flat) arch. In the same study, 0.21–0.28 was found to be normal in older adults.
What is the Arch Height Index (AHI) and why is there no class?
The AHI (Williams and McClay, Phys Ther 2000) is the dorsum height at half of total foot length divided by the truncated foot length, measured from the heel to the centre of the first metatarsophalangeal joint. There are no validated cut-offs for the AHI, so the tool only compares the value with a reference sample (mean and standard deviation). Different samples and measuring devices report different means.
Which measure is most valid?
In Menz and Munteanu's study of older adults (J Orthop Sports Phys Ther 2005), navicular height showed the strongest association with radiographic arch measures (r = 0.79); the arch index gave r = 0.52–0.71 and the FPI r ≈ 0.59. No single measure is enough on its own; a clinician combines measures with the examination, symptoms and gait.