---
title: "Foam Firmness Finder: Density, Firmness & Thickness"
url: "https://cushionguide.com/studio/foam-firmness-finder/"
---

*Five quick questions give the foam type, density, firmness and thickness for a bench, window seat, dining, floor, outdoor or sunbed cushion, with reasons.*

The Studio · Calculator

# Foam firmness finder

Five questions. Where it lives, who sits on it, how you like to sit, how thick it can be, how often it's used. You get the foam I'd cut for you — and the reasons, in plain words.

Worked out by [Callum](https://cushionguide.com/masters/callum/)

The Weather Man of Casco Bay · May 19, 2026

## The quick answer

Choose foam by two numbers, not one: density (lb/ft³ or kg/m³) decides how long it lasts, firmness (indentation hardness) decides how it feels. Everyday indoor seats suit high-resilience foam around 1.9–2.2 lb/ft³ (30–35 kg/m³) at 3–4 in; heavier sitters need a higher density or more thickness; outdoor cushions need open-cell dry-fast foam that drains.

## The foam firmness finder

Every field is live. Change a number and the drawing redraws; copy the link and it opens with your numbers.

Load an example — the ones marked are past projects

Drawing…

Cross-section to scale: cover, wrap, foam core and what sits under it — and roughly how far it gives.

## Buyer questions

## Soft sofa, firm facts

Two cushions, 41 by 26 inches, 5 inches thick, for a new sofa frame. The owner wanted to sink in, not perch, and asked whether thicker Dacron or extra fiber layers would do it.

They wouldn't, friend. Wrap softens the edges, not the seat. The workshop changed the foam instead: its softer 1.75 lb (28 kg/m³) grade in place of the standard 2.0 lb, same wrap, same thickness — three words in the order note.

**The lesson:** for lounging seats, change the foam, not just the thickness. Then check the density; softness bought with a very low grade wears out first.

## How to use it

Water-repellent is a promise; waterproof is a contract. Foam that holds rain is neither.

Same thickness, same soft edge, three colors: a side view that makes choosing a shade easier.

## Questions people ask

### What density foam is best for seat cushions?

For everyday indoor seats, high-resilience foam around 1.9–2.2 lb/ft³ (30–35 kg/m³) is a sound choice; go higher for heavy daily use or heavier sitters. Density is durability — it does not tell you how firm the foam feels.

### What is the difference between foam density and firmness?

Density is weight per volume and predicts how long the foam keeps its shape. Firmness — indentation force, ILD or IFD — is how hard it feels. A dense foam can be soft and a light foam can feel firm, so ask for both.

### How thick should a bench cushion be?

Most everyday benches get 3–4 in (7.5–10 cm). Next to a dining table, 2–3 in (5–7.5 cm) keeps the knees clear. Floor cushions need 4–6 in because there is no frame underneath to help.

### What foam is best for outdoor cushions?

Open-cell dry-fast (reticulated) foam, which drains instead of holding water, under a UV-resistant, water-repellent fabric. Standard foam in a water-repellent cover suits a covered porch, not open weather.

### Is memory foam good for bench cushions?

As a thin comfort layer on a supportive base, yes. On its own it is slow, warm and tends to bottom out on a hard bench; most seats are better with high-resilience foam.

Callum Reid

The Weather Man of Casco Bay · Portland, Maine

A former sailmaker who cut canvas for lobster boats and schooners on the Maine coast, then spent a few winters in the Florida Keys fixing sun-bleached boat cushions.

Fair winds — Callum

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